Waterborne gastroenteritis outbreak at a scouting camp caused by two norovirus genogroups: GI and GII

Background: A cross-border gastroenteritis outbreak at a scouting camp was associated with drinking water from a farmer's well. Objectives: A retrospective cohort study was performed to identify size and source of the outbreak, as well as other characteristics. Study design: Epidemiological investigation included standardized questionnaires about sex, age, risk exposures, illness and family members. Stool and water (100 mL) samples were analyzed for bacteria, viruses and parasites. Results: Questionnaires were returned by 84 scouts (response rate 82%), mean age of 13 years. The primary attack rate was 85% (diarrhoea and/or vomiting). Drinking water was the strongest independent risk factor showing a dose-response effect with 50%, 75%, 75%, 93% and 96% case prevalence for 0, 1, 2-3, 4-5 and >5 glasses consumed, respectively. Norovirus (GI.2 Southampton and GII.7 Leeds) was detected in 51 stool specimens (75%) from ill scouts. Water analysis showed fecal contamination, but no norovirus. The secondary attack rate was 20%. Conclusions: This remarkable outbreak was caused by a point-source infection with two genogroups of noroviruses most likely transmitted by drinking water from a well. Finding a dose-response relationship was striking. Specific measures to reduce the risk of waterborne diseases, outbreak investigation and a good international public health network are important. (C) 2009 Elsevier B. V. All rights reserved.