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A large community outbreak of norovirus (NV) gastrointestinal infection occurred in Västra Götaland County, Sweden in August 2004, following attendance at recreational lakes. A frequency age-matched case control study was undertaken of persons who had attended these lakes to identify risk factors. 163 cases and 329 controls were included. Analysis indicates that having water in the mouth while swimming (OR=4.7; 95% CI 1.1-20.2), attendance at the main swimming area at Delsjön Lake (OR=25.5; 95% CI 2.5-263.8), taking water home from a fresh water spring near Delsjön lake (OR=17.3; 95% CI 2.7-110.7) and swimming less than 20 m from shore (OR=13.4; 95% CI 2.0-90.2) were significant risk factors. The probable vehicle was local contamination of the lake water (especially at the main swimming area). The source of contamination could not be determined.

Original publication





Scandinavian journal of infectious diseases

Publication Date





323 - 331


European Programme for Intervention Epidemiology Training (EPIET), Solna, Sweden.


Humans, Norovirus, Caliciviridae Infections, Gastroenteritis, Health Surveys, Risk Factors, Case-Control Studies, Fresh Water, Disease Outbreaks, Swimming, Recreation, Adolescent, Adult, Child, Child, Preschool, Infant, Sweden, Female, Male