Y pseudotuberculosis infections traced to lettuce

Feb 24, 2004 (CIDRAP News) – An unusual intestinal infection that is often mistaken for appendicitis has been traced to a specific food source, iceberg lettuce, for the first time, according to a report in the Mar 1 Journal of Infectious Diseases (JID).

Yersinia pseudotuberculosis infections cause fever and abdominal pain but are relatively rare in humans, according to the report by a group of Finnish investigators led by J. Pekka Nuorti. Veterinarians know the pathogen—a close relative of Yersinia pestis, the cause of plague—for causing illness in hares, deer, sheep, and various other animals.

In October 1998, routine surveillance of laboratory-diagnosed infections in Finland revealed an alarming increase in Y pseudotuberculosis infections, the report says. Nuorti and colleagues identified 47 case-patients and enrolled 38 of them in a case-control study. Patients were significantly more likely than controls to have eaten iceberg lettuce, and the risk of infection increased with the amount of lettuce consumed. All 27 Y pseudotuberculosis isolates obtained from patients were matched by molecular fingerprinting (pulsed-field gel electrophoresis).

The epidemiologic investigation led to four cafeterias where the patients reported having eaten lettuce. "The lettuce served in those cafeterias was traced to four farms in the southwest archipelago region of Finland," states a news release from the Infectious Diseases Society of America, publisher of JID. "While no lettuce remained from the shipments identified from the cafeterias, Y. pseudotuberculosis was discovered in soil, irrigation water, and lettuce samples from one of those farms. The investigators suspect that the pathogen was spread by the feces of roe deer, which have been carriers of the pathogen in the past."

In an editorial accompanying the report, Robert V. Tauxe of the US Centers for Disease Control and Prevention writes that Y pseudotuberculosis has been thought to be a foodborne pathogen but that this had never been clearly confirmed. A large Canadian outbreak in 1998 was epidemiologically linked to pasteurized milk, but the specific source was never found, he writes, adding, "The Finnish investigationis the first tolink an outbreak ofhuman illness to alikely environmental reservoir viacontaminated food."

Tauxe writes that preventing lettuce-related Y pseudotuberculosis infections will require determining whether the microbe is taken up by the plant and identifying the pathogen's animal reservoir. "Prevention mayultimately involve fences andanimal population control orvaccination, as well asthe use of disinfectedwater in washing orprocessing," he states.

Nuorti JP, Niskanen T, Hallanvuo S, et al. A widespread outbreak of Yersinia pseudotuberculosis O:3 infection from iceberg lettuce. J Infect Dis 2004;189(5):766-74 [Abstract]

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