22 September 2005
EHEC O157 outbreak in Sweden from locally produced lettuce,
Ann Söderström1 (firstname.lastname@example.org),
Anders Lindberg2, and Yvonne Andersson3
1Smittskyddsenheten (Department of Communicable Disease
Control) Västra Götaland, Sweden
2Smittskyddsenheten (Department of Communicable Disease Control) Halland,
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
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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