context: On 6 June 2019, the Norwegian Institute of Public  Health was notified of more than 50 cases of gastroenteritis in Asky.
  On the evening of 6 June 2019, the Medical Officer in  Asky reported an outbreak of gastroenteritis to the  NIPH.
  In Norway, outbreaks of campylobacteriosis  have been associated with consumption of untreated  or contaminated drinking water, unpasteurised milk,  mutton, contact with farm animals and with butcher- ing, preparation and consumption of poultry [4-6].
  Contamination through cracks in the reservoir most  probably occurred during heavy rainfall.
  While we were  unable to conclusively determine how the reservoir  became contaminated, the diversity of data sources  used to investigate this outbreak support the hypothesis that environmental contamination through cracks  in Reservoir X most likely occurred during heavy rain- fall following a long dry period.
  Campylobacter has frequently been identified as the  cause of waterborne outbreaks, often associated with heavy rainfall and intrusion of  contaminated surface water either into source water or into the distribution network.
  A reservoir in a water supply sys- tem was suspected as the source of the outbreak  because of the acute onset and geographical distri- bution of cases.
  In Norway, outbreaks of campylobacteriosis  have been associated with consumption of untreated  or contaminated drinking water, unpasteurised milk,  mutton, contact with farm animals and with butchering, preparation and consumption of poultry [4-6].
  Staff  of the OPHS noted that many patients presenting with  gastroenteritis had home addresses near each other,  which led to a suspicion that drinking water could be  the source of the outbreak.
  On the evening of 6 June 2019, the Medical Officer in  Asky reported an outbreak of gastroenteritis to the  NIPH.
  On 6 June 2019, the Norwegian Institute of Public  Health was notified of more than 50 cases of gastroenteritis in Asky.
  In a 24 h period, 10 people had been hospitalized with fever, abdominal pain and diarrhoea, and ca 30 individuals had sought medical attention from out- of-hours primary healthcare services (OPHS).
  The overall attack rate was 20%  for the childcare centres in affected areas and 2% for  the childcare centres in unaffected areas.
  In a 24 h period, 10 people had been hospitalized with fever, abdominal pain and diarrhoea, and ca 30 individuals had sought medical attention from out- of-hours primary healthcare services (OPHS).
  For the childcare centre  survey, a case was defined as any person absent from  the childcare centre (child or employee) because of the  symptoms diarrhoea or vomiting between 28 May and  7 June.
  We defined a case as a person with gastroenteritis (defined as having symptoms of (i) diarrhoea  only or (ii) vomiting and at least one of the following:  abdominal distention, fever, stomach pain or nausea,  with duration of illness of more than 24 h), with symptom onset between 1 and 19 June 2019.
  They  reported  diarrhoea, stomach pain and fever with onset on 4 June  (n = 1) or 5 June (n = 4).
  A total of 1,829 persons reported at least one of the fol- lowing symptoms: diarrhoea (n = 1,626; 89%), abdominal pain (n = 1,347; 74%), headache (n = 959; 52%),  nausea (n = 935; 51%), fever (n = 868, 48%), abdominal  distention (n = 639; 35%), vomiting (n = 286; 16%) and  bloody stool (n = 113; 6%).
  We conducted pilot interviews, a  telephone survey and an SMS-based cohort study of  residents served by WSS-A.
  Whole genome sequencing on  human and environmental isolates was performed.  
  In order to determine the extent of the outbreak, we  collected data on in-person and telephone consultations with the International Classification of Primary  Care (ICPC-2) codes for diarrhoea (D11), gastrointestinal  infection (D70) and gastroenteritis (D73) that occurred  at the OPHS and general practitioners (GP) offices  in Asky between 3 June and 15 June.
  Several  of  the  initial  cases  with  confirmed Campylobacter infections were interviewed  using a standardized 19-page trawling questionnaire in  order to exclude possible exposures other than drinking water.
  A case was defined as a person in  a household served by Water Supply System A (WSS- A) who had gastroenteritis for more than 24 h between  1 and 19 June 2019.
  The  primary  diagnostic  laboratory  sent Campylobacter isolates from patients to the  National Reference Laboratory for Enteropathogenic  Bacteria (NRL) for confirmation and genotyping.
  According to the routine sampling and analysis plan for  WSS-A, water samples are collected and tested for faecal indicator bacteria: weekly for Escherichia coli and  coliform bacteria and for heterotrophic plate count,  and monthly for intestinal enterococci and Clostridium  perfringens, according to standard methods described  in the national drinking water legislation [21].
  Mean age of the included household members was  34 years (range: 0 to 93 years) and 50% were female.
  
answers: {'answer_start': [1666], 'text': ['drinking water']}