Outbreak of Salmonella Thompson infections linked to imported rucola lettuce

Karin Nygård*, Jørgen Lassen, Line Vold, Yvonne Andersson, Ian Fisher, Sven Löfdahl, John Threlfall, Ida Luzzi, Tansy Peters, Michael Hampton, Mia Torpdahl, Georg Kapperud, Preben Aavitsland

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

120 Citations (Scopus)


On November 15, 2004, a cluster of three cases of Salmonella Thompson infection was registered by the Norwegian reference laboratory. In the following days further cases occurred, prompting a case-control study among the first 13 cases and 26 matched controls. By December 31, 21 cases had been reported, with the first onset on October 24. Consumption of rucola lettuce (Eruca sativa, also known as rocket salad or arugula) (OR 8,8 [1,2-∞]) and mixed salad (OR 5,0 [1,0-∞]) was associated with illness. On November 26, Swedish authorities notified the finding of Salmonella Thompson in rucola lettuce through the EU Rapid Alert System for Food and Feed. Later, several countries reported finding this and other Salmonella serovars and Campylobacter in rucola produced in Italy. In response to our alert through the international Enter-net surveillance network, Sweden and England also reported an increase of cases. Salmonella Thompson isolates from products and patients from several countries showed high similarity by pulsed-field gel electrophoresis, but some isolates showed significant differences. We think that the outbreak in Norway reflected a larger international outbreak caused by rucola imported from one Italian producer. Findings of other pathogens indicate a massive contamination, possibly caused by irrigation with nonpotable water. Rapid international information exchange is invaluable when investigating outbreaks caused by internationally marketed products.

Original languageEnglish
Pages (from-to)165-173
Number of pages9
JournalFoodborne pathogens and disease
Issue number2
Publication statusPublished - 1 Apr 2008


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