Y. pseudotuberculosis, first identified in 1883, causes infections characterized by fever and abdominal pain that are often confused with acute appendicitis. The microbe is well known in veterinary medicine as the cause of illnesses in hares, deer, and sheep, among other animals. Y. pseudotuberculosis infections in humans are relatively rare, and while foodborne transmission has long been suspected, attempts to trace the pathogen to a concrete source of contamination in the past have been unsuccessful.

In October of 1998, two microbiology laboratories in southern Finland discovered an alarming increase in infections during routine surveillance of laboratory-diagnosed infections. J. Pekka Nuorti, of the National Public Health Institute of Finland, and colleagues from the University of Helsinki, the National Public Health Institute of Finland, and the National Food Agency of Finland initiated epidemiological and environmental investigations that would eventually reveal the source as contaminated iceberg lettuce.

In a case-control study, 38 patients with confirmed infections were questioned about what and where they ate in the two weeks before the onset of their symptoms. The investigation led to four lunch cafeterias where the patients reported eating iceberg lettuce. The lettuce served in those cafeterias was traced to four farms in the southwest archipelago region of Finland. 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
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Contact: Diana Olson
dolson@idsociety.org
703-299-0200
Infectious Diseases Society of America
17-Feb-2004