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Home Eurosurveillance Weekly Release  2005: Volume 10/ Issue 38 Article 1
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Eurosurveillance, Volume 10, Issue 38, 22 September 2005

Citation style for this article: Söderström A, Lindberg A, Andersson Y. EHEC O157 outbreak in Sweden from locally produced lettuce, August-September 2005. Euro Surveill. 2005;10(38):pii=2794. Available online:

EHEC O157 outbreak in Sweden from locally produced lettuce, August-September 2005

Ann Söderström1 (, Anders Lindberg2, and Yvonne Andersson3

1Smittskyddsenheten (Department of Communicable Disease Control) Västra Götaland, Sweden
2Smittskyddsenheten (Department of Communicable Disease Control) Halland, Sweden
3Swedish Institute for Infectious Disease Control, Stockholm, Sweden

An outbreak of enterohaemorrhagic Escherichia coli (EHEC) O157 VT2 infections is known to have affected 120 people on the west coast of Sweden (Halland and Västra Götaland counties) between 16 August and 10 September 2005. The outbreak was first identified at the end of August when about 10 cases were notified. To date (20 September), about 120 cases have been confirmed by culture, and pulsed-field gel electrophoresis (PFGE) has shown one dominant strain. Most of the patients were women. Seven people have developed haemolytic uraemic syndrome. A few people in other parts of Sweden became ill due to infection with the dominant outbreak strain during this period.

An intense investigation into the source of the infection was undertaken by the communicable disease control departments in Västra Götaland and Halland, in cooperation with the local environmental health agencies and the Smittskyddsinstitutet (Swedish Institute for Infectious Disease Control, SMI) in Sweden. The patients were mostly women (ratio 2 men to 3 women) and a few patients were children. The patients were contacted and interviewed about foods consumed in the seven days before onset of symptoms.

Descriptive epidemiology suggested a link between infection and the consumption of iceberg lettuce. This association was confirmed using a case control study, which showed an odds ratio of 13 for consumption of lettuce and illness. Trace back investigations implicated a local lettuce producer. The implicated crop was irrigated using water from a small stream. It was possible to link cases from other parts of Sweden to either consumption of lettuce from the implicated producer or travel to the west coast.

Food and environmental investigations continue with lettuce, water and environmental samples being examined for the presence of the outbreak strain. The lettuce was removed from sale on 9 September. Since 10 September, there have been no new cases detected in connection with this outbreak.

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