Epidemiology and Infection

Swimming-associated outbreak of Escherichia coli O157[ratio]H7

M. PAUNIO a1, R. PEBODY a2 1 , M. KESKIMÄKI a3, M. KOKKI a2, P. RUUTU a2, S. OINONEN a4, V. VUOTARI a5, A. SIITONEN a3, E. LAHTI a6 and P. LEINIKKI a2c1
a1 University of Helsinki, Department of Public Health, Mannerheimintie 172, P.O. Box 41 (00014 University of Helsinki), Finland
a2 National Public Health Institute, Department of Infectious Disease Epidemiology, Mannerheimintie 166, (00300 Helsinki 30) Finland
a3 National Public Health Institute, Laboratory of Enteric Pathogens, Mannerheimintie 166, (00300 Helsinki 30), Finland
a4 Central Hospital of Seinäjoki, Hanneksenrinne 7, 60220 Seinäjoki, Finland
a5 Alavus Health Centre, Salmentie 10, 63300 Alavus, Finland
a6 National Veterinary and Food Research Institute P.O. Box 368, 00231 Helsinki 23, Finland


In 1997 the first outbreak of Escherichia coli O157[ratio]H7 infections involving 14 cases occurred in Finland. A case was defined as a resident of Alavus with an episode of diarrhoea between 5 and 17 July 1997, and from whom E. coli O157[ratio]H7 was isolated from stool. The investigation included case searching and a population-based case control study. Five primary and eight symptomatic secondary cases of E. coli O157[ratio]H7 illness were detected. In the 10 days before the outbreak, all 5 primary patients (aged 3–8 years), but only 6 of 32 population controls from the same age range (Fisher's test, P<0·001) and 4 of 10 sibling controls (P<0·05) had visited (but had not necessarily bathed in) a shallow beach popular among young children. Four out of 5 primary cases had remained within 5 m of the beach while swimming and had swallowed lake water compared to 1 of 5 population controls. These analytical epidemiologic findings incriminated fresh lake water as the vehicle of E. coli O157[ratio]H7 transmission.

(Accepted August 19 1998)

c1 Author for correspondence.


1 European Programme of Intervention Epidemiology Training.