An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.

{'answer_start': [2584], 'text': ['diarrhoea or vomiting']}