Epidemiology and Infection

A Norwalk-like virus waterborne community outbreak in a Swedish village during peak holiday season

a1 Swedish Institute for Infectious Disease Control, 17182 Solna, Sweden
a2 European Programme for Intervention Epidemiology Training (EPIET), 17182 Solna, Sweden
a3 Dalarna County Council of Communicable Disease Control, Falu lasarett, 79182 Falun, Dalarna, Sweden

Article author query
carrique-mas j   [PubMed][Google Scholar] 
andersson y   [PubMed][Google Scholar] 
petersen b   [PubMed][Google Scholar] 
hedlund k-o   [PubMed][Google Scholar] 
sjogren n   [PubMed][Google Scholar] 
giesecke j   [PubMed][Google Scholar] 


An outbreak of gastroenteritis due to Norwalk-like virus (NLV) affecting approximately 500 people occurred in a Swedish ski resort during February–March 2002. Epidemiological investigations were performed on cohorts of schoolchildren, permanent residents and skiers visiting the area. Attack rates were respectively 39·7, 29·9 and 38·5%. Drinking un-boiled water originating from one of the three communal water systems was a significant risk factor for all groups. For schoolchildren, the risk of illness increased with increasing amount of water consumed. Nine of 12 stool samples of patients analysed tested positive for NLV. The water tested negative for indicator bacteria and results of NLV tests were inconclusive. In the absence of microbiological findings, the environmental authorities were reluctant to act based on the epidemiological analysis alone, and intervention was delayed until mid-April, following the discovery of a crack in a sewage pipe 10 m from the well.

(Accepted February 14 2003)

c1 Ecology and Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, U.K.