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Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What symptoms did the people had?

{'answer_start': [3200], 'text': ['acute gastroenteritis']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What type of samples were analyzed?

{'answer_start': [1835], 'text': ['stool samples']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What caused the event?

{'answer_start': [4357], 'text': ['heavy faecal contamination of the raw water from Gta lv river']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What symptoms did people report?

{'answer_start': [1760], 'text': ['acute gastroenteritis']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What were the first steps of investigation?

{'answer_start': [1590], 'text': ['questionnaires']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the date of the event?

{'answer_start': [71], 'text': ['2008']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the location of the event?

{'answer_start': [61], 'text': ['Sweden']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What pathogen was connected to the outbreak?

{'answer_start': [3738], 'text': ['faecal indicator bacteria and coliphages']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the source that started the event?

{'answer_start': [4224], 'text': ['contaminated drinking water']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

How was the event first detected?

{'answer_start': [152], 'text': ['unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

How many people were ill?

{'answer_start': [3069], 'text': ['2000']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What are the pathogens?

{'answer_start': [3119], 'text': ['NoV']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the concentration of the contaminant after analysis?

{'answer_start': [3780], 'text': ['300 plaque- forming units (p.f.u.)/100 ml']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What are the symptoms?

{'answer_start': [222], 'text': ['gastrointestinal symptoms']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the concentration of the pathogen?

{'answer_start': [3924], 'text': ['between 4 and 42 p.f.u./100 ml']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the event?

{'answer_start': [0], 'text': ['A large waterborne outbreak of NoV']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What are the initial steps of investigation?

{'answer_start': [786], 'text': ['identify the causative agents, the extent of the outbreak and possible sources of infection']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What are the first steps of mitigation?

{'answer_start': [699], 'text': ['boil water recommendation']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What type of samples were examined?

{'answer_start': [2041], 'text': ['Water samples']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What did the authorities do to mitigate the event?

{'answer_start': [905], 'text': ['inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms.']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What was the age of the affected people?

{'answer_start': [1697], 'text': ['19 and 75 years']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What is the source of contamination?

{'answer_start': [644], 'text': ['drinking water']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What was the alert of the event?

{'answer_start': [1308], 'text': ['notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms']}

Contamination Question Answering

A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20].

What were the associated pathogens of concern?

{'answer_start': [3389], 'text': ['Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples.']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What type of samples were analyzed?

{'answer_start': [461], 'text': ['Stool specimens']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What caused the event?

{'answer_start': [1380], 'text': ['contamination of a coastal lagoon']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What symptoms did people report?

{'answer_start': [2333], 'text': ['vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the initial cause of the event?

{'answer_start': [591], 'text': ['sewage contamination event impacting the lagoon']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the date of the event?

{'answer_start': [125], 'text': ['January 2017']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the location of the event?

{'answer_start': [111], 'text': ['South Africa']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What pathogen was connected to the outbreak?

{'answer_start': [2558], 'text': ['Aeromonas, enterovirus and EPEC']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the source that started the event?

{'answer_start': [2936], 'text': ['lagoon']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

How was the event first detected?

{'answer_start': [51], 'text': [' reported by healthcare workers']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

How many people were ill?

{'answer_start': [2183], 'text': ['311 cases']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What are the pathogens?

{'answer_start': [2485], 'text': ['NoV']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the concentration of the contaminant after analysis?

{'answer_start': [2709], 'text': ['The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What are the symptoms?

{'answer_start': [917], 'text': ['diarrhoea and/or vomiting']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the concentration of the pathogen?

{'answer_start': [2848], 'text': ['The E. coli level was 1.93* 10^3 cfu/100 ml']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the event?

{'answer_start': [26], 'text': ['gastroenteritis cases was reported by healthcare workers']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What are the initial steps of investigation?

{'answer_start': [181], 'text': ['A case-control study was conducted']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the duration of the event?

{'answer_start': [1043], 'text': ['between 14 December 2016 and 5 January 2017']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

From when until when the event happened

{'answer_start': [1529], 'text': ['during December 2016 and January 2017']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What type of samples were examined?

{'answer_start': [1996], 'text': ['Water samples']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What was the age of the affected people?

{'answer_start': [2260], 'text': ['21 years']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What is the source of contamination?

{'answer_start': [632], 'text': ['lagoon']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What was the alert of the event?

{'answer_start': [736], 'text': ['the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms']}

Contamination Question Answering

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon.

What were the associated pathogens of concern?

{'answer_start': [2616], 'text': ['NoV GI']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What is the initial cause of the event?

{'answer_start': [3461], 'text': ['run-off of rainwater contaminated with faeces of breeding gulls']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What is the date of the event?

{'answer_start': [3], 'text': ['May 2007']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What is the location of the event?

{'answer_start': [82], 'text': ['North Holland']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

How was the event first detected?

{'answer_start': [2412], 'text': ['samples']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What are the pathogens?

{'answer_start': [2387], 'text': ['E. coli']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What are the first steps of mitigation?

{'answer_start': [146], 'text': ['boil tap water']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What did they do to mitigate the event?

{'answer_start': [2912], 'text': ['public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What did the authorities do to mitigate the event?

{'answer_start': [2786], 'text': ['broadcasted through mass-media including the national and regional television channel, radio and newspapers.']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What is the source of contamination?

{'answer_start': [46], 'text': ['tap water']}

Contamination Question Answering

In May 2007, Escherichia coli was detected in tap water supplied by a company in North Holland. The company issued advice through mass media to boil tap water before consumption; this advice was lifted six days later. A cross-sectional study was implemented to investigate compliance among residents in this area. Based on postcode, a total of 300 households, chosen randomly from a database of a private company performing internet-based surveys for different marketing purposes, were sent a self-administered questionnaire for this study. The questionnaire contained questions on demographic information, source of information regarding the advice, response to it and personal opinions on the companys reaction and the advice. Ninety-nine (66%) households of the affected area and 90 (60%) households from non-affected areas served by the same company replied to the survey. All respondents knew about the advice. 81.8% of the respondents in the affected area and 5.6% of the non-affected areas reported complying with the advisory. Most respondents from the affected area still used unboiled water to brush teeth, wash salads and fruits. There was no difference in compliance between men and women. Using the mass media was proved to be efficient to inform the public and could be used in the future in similar settings. However, more detailed wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease which can be prevented by protection of the source water, efficient treatment processes and reliable distribution systems. The European Union Drinking Water Directive [1] demands monitoring of tap water for different parameters, such as Escherichia coli, to indicate possible faecal contamination from humans and animals. System failure or human error may cause an increase in the level of pathogens in the water posing a risk of waterborne disease. For example, in 2001, a large outbreak of gastroenteritis occurred due to accidental introduction of partially treated water to the drinking water supply system in the Netherlands, resulting in 921 households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking water company may issue an advice to boil tap water before using it for domestic purposes. On 15 May 2007, E. coli was detected in samples collected the day before of the finished tap water delivered by a company in the province Noord-Holland (North-Holland) in the Netherlands. For preventive reasons, on the same day the company issued an advice for consumers to boil tap water for two minutes before consumption but that this was not necessary for taking a shower or washing. This information was broadcasted through mass-media including the national and regional television channel, radio and newspapers. In addition, a public website used during emergency situations (www.crisis.nl) and a toll-free telephone number were made available for the public to provide information to households in the affected area. The boil water advice had an impact on approximately 180,000 households in the affected area comprising 13 municipalities. The advice was lifted a week later, on 22 May 2007, as risk for public health was no longer present. In September 2007, the water company published a press release informing that the cause of the water contamination was due to run-off of rainwater contaminated with faeces of breeding gulls on the roof that had seeped into one of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may represent a public health risk. For this reason, we investigated compliance with boil water advice issued by the private water company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors that may have affected water consumption habits of the residents in the area supplied by the water company. For this purpose, on the companys behalf, a self-administered questionnaire was sent to 300 households in June 2007. Households were selected on the basis of their residence postcodes; half in the area where the advice was valid and half in areas served by the same company but where the advice did not apply. These participants were derived from a database of a private company that conducts online consumer surveys for marketing purposes. The questionnaire contained questions on demographic information, level of urbanisation, source and time of receiving the information regarding the advice, initial and secondary response to the advice and personal opinions on the companys response and the advice itself. The data were sent back to the drinking water company and the National Institute for Public Health and the Environment, where they were analysed. The statistical analysis was done with STATA v10. 2 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water contamination and 90 households (60%) from control areas supplied with water by the same company replied to the survey. Women more often than men responded to the questionnaire in both the affected and the non-affected areas (57.7% of all responders). The respondents represented 189 households with a total population of 505 people, 176 (34.9%) of whom were below the age of 18 years. There was no statistically significant difference in the number of children per household between the affected and the non-affected areas (p=0.112). Descriptive results for the two different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that they had been informed about the advice. Ninety-five (50.3%) of them said they had first heard about it through the television. Other sources were radio (24.3%), friends, relatives or neighbours (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently disappointed (14.1%) about the choice of the company to use mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the respondents had first reacted with fear to the information on the possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The corresponding percentages for the non affected area were 15.7%, 72.9% and 11.4%. About half (48.5%) of the respondents from the affected area said they had looked for more information when they had heard about the advice, while the corresponding proportion of respondents from the non-affected area was only 8.9% (p<0.001). The most common source of active search for more information was the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said they had complied with the advice. This was done by buying bottled water (43.4% of all respondents in affected area) or boiling tap water for two minutes before consuming it (70.7%). None of the respondents in the area stopped consuming tap water completely. Five (5.6%) of the respondents in the non-affected area were buying bottled water and three of them (3.3%) were boiling tap water during the advice. These numbers were considerably lower than the corresponding ones in the affected area, but showed that compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities such as washing and showering, 26 (26.3%) of the respondents in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177 respondents (93.7%) thought that the company had done well informing the consumers about the water contamination and its response to it. This prevailing opinion was not different between respondents from the affected area and those from the non affected area. The respondents compliance with the advice was independent of sex, age and the presence of children in the household. However, the respondents were 138.6 times more likely to follow the advice if a second person in the household was following it as well (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled water for uses other than drinking, too. These results are shown in Table 3. The majority of the respondents stated that their image of the company had not changed after the incident and the six-day advice (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected area found out about the advice played no significant role in the subsequent compliance of the respondents. The highest compliance rates occurred among those in the affected area who heard about the advice from the internet (90%) or from friends (89.5%). Respondents informed by more than one source were more likely T a b l e 1 Survey on boil water advice in the North Holland province in the Netherlands, 2007, demographic characteristics of the respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age (years) 47.7 48.4 48.0 0.7549 Number of people living in the household 2.62 2.82 2.72 0.2526 Number of children living in the household 0.78 1.11 0.93 0.0510 T a b l e 2 Reasons for non-compliance with boil water advice in the affected area in the North Holland province, the Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e 3 Use of boiled water for uses other than drinking in the affected area in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4 EUROSURVEILLANCE Vol. 14 Issue 12 26 March 2009 www.eurosurveillance.org 3 to have complied with the advice (90.9% against 79.2%) but this difference was not statistically significant. The source of information did not depend on the age (p=0.6532). Compliance with the advice did not differ between households with children and those without children (p=0.536). Respondents who undertook active search for more information may have been more likely to follow the advice than those who did not proceed to further active search for more information (89.4% vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible to estimate unwitting compliance rates.

What were the associated pathogens of concern?

{'answer_start': [13], 'text': ['Escherichia coli']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What symptoms did the people had?

{'answer_start': [4068], 'text': ['diarrhea']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What symptoms were developed?

{'answer_start': [6940], 'text': ['diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What caused the event?

{'answer_start': [18031], 'text': ['animal feces']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

With what symptoms they were presented?

{'answer_start': [4217], 'text': ['diarrhea']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What symptoms did people report?

{'answer_start': [3962], 'text': ['diarrhea']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What were the first steps of investigation?

{'answer_start': [5622], 'text': ['rainfall statistics']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the date of the event?

{'answer_start': [108], 'text': ['March 2000']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the location of the event?

{'answer_start': [82], 'text': ['northwest England']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What pathogen was connected to the outbreak?

{'answer_start': [216], 'text': ['Cryptosporidium oocysts']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

How was the event first detected?

{'answer_start': [3012], 'text': ['Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority.']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

How many people were ill?

{'answer_start': [120], 'text': ['Fifty-eight cases']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the attack rate?

{'answer_start': [7207], 'text': ['29.6 per 10,000 population']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What are the pathogens?

{'answer_start': [155], 'text': ['Cryptosporidium']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the concentration of the contaminant after analysis?

{'answer_start': [10252], 'text': ['76 oocysts of Cryptosporidium per 1,000 L']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What are the symptoms?

{'answer_start': [141], 'text': ['diarrhea']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the concentration of the pathogen?

{'answer_start': [10436], 'text': ['five oocysts per 10 L of water']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the event?

{'answer_start': [0], 'text': ['An outbreak of cryptosporidiosis']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What are the initial steps of investigation?

{'answer_start': [3587], 'text': ['interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire ']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What was the age of the affected people?

{'answer_start': [6787], 'text': ['from 7 months to 95 years, but most patients were ‹5 years']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What is the source of contamination?

{'answer_start': [17753], 'text': ['water supply']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

How many cases were there?

{'answer_start': [6469], 'text': ['Fifty-eight cases']}

Contamination Question Answering

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed. Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe. In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made. The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days. *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping. Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings. After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21. Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool. Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases, Clitheroe, 2000. Table 1. Age-specific attack rates for cryptosporidiosis in residents of water zone 97, Clitheroe, March 2000 Age group Cases (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak. The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls. On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident). Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range of water works during investigationa of cryptosporidial outbreak, Clitheroe, March 16April 6, 2001 Date Samples taken Samples positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples. The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps. Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone. At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3. Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10). The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard. The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able. Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence.

What were the associated pathogens of concern?

{'answer_start': [5228], 'text': ['Cryptosporidium oocysts']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What type of samples were analyzed?

{'answer_start': [1130], 'text': ['faecal sample']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

With what symptoms they were presented?

{'answer_start': [2517], 'text': ['diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%)']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What were the first steps of investigation?

{'answer_start': [1369], 'text': ['A standardized questionnaire ']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the initial cause of the event?

{'answer_start': [5453], 'text': ['water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the date of the event?

{'answer_start': [3], 'text': ['August 2003']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the location of the event?

{'answer_start': [121], 'text': ['southwest England.']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

How was the event first detected?

{'answer_start': [299], 'text': ['Following an earlier complaint from a visitor about the water quality']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

How many people were ill?

{'answer_start': [2332], 'text': ['Sixty three children (89%)']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

How many people were hospitalized?

{'answer_start': [2779], 'text': ['Ten children (16%)']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the attack rate?

{'answer_start': [4831], 'text': ['89% in the cohort studied']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What are the pathogens?

{'answer_start': [505], 'text': ['E.coli']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the concentration of the contaminant after analysis?

{'answer_start': [486], 'text': ['2100 coliforms, 40�E.coli�per cu mm']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What are the symptoms?

{'answer_start': [1010], 'text': ['diarrhoea, blood in stools, vomiting, nausea, or abdominal pain']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What is the event?

{'answer_start': [18], 'text': ['outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What are the initial steps of investigation?

{'answer_start': [524], 'text': ['A cohort study']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What type of samples were examined?

{'answer_start': [2021], 'text': ['Faecal samples from the farmyard animals']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

For which pathogens did they test for in the samples?

{'answer_start': [1877], 'text': ['Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What measures were taken to prevent the event?

{'answer_start': [5790], 'text': ['reviewed and revised health and safety risk assessments']}

Contamination Question Answering

In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park. Methods The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study. Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed. Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping. Results Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission. Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE]. Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park. The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation. Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium. Discussion This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection. In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

What was the age of the affected people?

{'answer_start': [2452], 'text': ['Median age was 6 years (range 1-15).']}

Contamination Question Answering

In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health (2017) 17:328 DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health (2017) 17:328 Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health (2017) 17:328 Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i max L; V ; V Et;i L SDt;i; L 3; 5 f g Et;i pt;i Ni; SDt;i Ni pt;i q 1pt;i; pt;i Pni j1;ji P C;j 10 Pni j1;jiNj ; t7; t8; t9; t10; t11; t12; t13; t14 f g; 2; if t7; t14 f g 1; if t8; t9; t10; t11; t12; t13 f g where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health (2017) 17:328 Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health (2017) 17:328 Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239 53,997 73.7 Cases 18,448 1191 16,114 20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health (2017) 17:328 Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66 6.68 <0.001 6-15 2.28 1.42 3.68 0.001 16-65 3.08 1.96 4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49 3.56 <0.001 Not Abborrverket WTP 1.14 0.68 1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195 2671 62.8 6-15 5542 208 5135 5950 75.3 16-65 30,728 1148 28,479 32,977 69.6 66- 12,914 326 12,276 13,553 87.9 Cases 0-5 1442 120 1207 1676 37.2 6-15 1819 202 1423 2215 24.7 16-65 13,402 1132 11,183 15,621 30.4 66- 1786 301 1196 2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health (2017) 17:328 Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392 23,906 83.8 Abborrverket WTP 28,696 1033 26,944 30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145 5590 16.2 Abborrverket WTP 14,081 1019 12,084 16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4 84.7 Abdominal pain 73.3 66.8 79.8 Upset stomach 71.4 64.7 78.2 Diarrhoea Watery 70.2 63.4 77.0 Bloody 0.9 0.0 2.5 Nausea 63.5 56.1 70.9 Headache 46.9 39.3 54.5 Vomiting 35.8 28.6 43.1 Fever >38 C 36.5 28.2 42.8 Joint pain 27.4 20.4 34.4 Pain in eyes 14.6 9.1 20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health (2017) 17:328 Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

What type of samples were analyzed?

{'answer_start': [7915], 'text': ['Fecal samples from patients']}

Contamination Question Answering

In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health (2017) 17:328 DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health (2017) 17:328 Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health (2017) 17:328 Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i max L; V ; V Et;i L SDt;i; L 3; 5 f g Et;i pt;i Ni; SDt;i Ni pt;i q 1pt;i; pt;i Pni j1;ji P C;j 10 Pni j1;jiNj ; t7; t8; t9; t10; t11; t12; t13; t14 f g; 2; if t7; t14 f g 1; if t8; t9; t10; t11; t12; t13 f g where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health (2017) 17:328 Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health (2017) 17:328 Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239 53,997 73.7 Cases 18,448 1191 16,114 20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health (2017) 17:328 Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66 6.68 <0.001 6-15 2.28 1.42 3.68 0.001 16-65 3.08 1.96 4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49 3.56 <0.001 Not Abborrverket WTP 1.14 0.68 1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195 2671 62.8 6-15 5542 208 5135 5950 75.3 16-65 30,728 1148 28,479 32,977 69.6 66- 12,914 326 12,276 13,553 87.9 Cases 0-5 1442 120 1207 1676 37.2 6-15 1819 202 1423 2215 24.7 16-65 13,402 1132 11,183 15,621 30.4 66- 1786 301 1196 2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health (2017) 17:328 Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392 23,906 83.8 Abborrverket WTP 28,696 1033 26,944 30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145 5590 16.2 Abborrverket WTP 14,081 1019 12,084 16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4 84.7 Abdominal pain 73.3 66.8 79.8 Upset stomach 71.4 64.7 78.2 Diarrhoea Watery 70.2 63.4 77.0 Bloody 0.9 0.0 2.5 Nausea 63.5 56.1 70.9 Headache 46.9 39.3 54.5 Vomiting 35.8 28.6 43.1 Fever >38 C 36.5 28.2 42.8 Joint pain 27.4 20.4 34.4 Pain in eyes 14.6 9.1 20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health (2017) 17:328 Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

What were the first steps of investigation?

{'answer_start': [363], 'text': ['epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources.']}