Yersiniosis Associated with Tofu Consumption: Serological, Biochemical and Pathogenicity Studies of Yersinia enterocolitica Isolates

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Abstract
From December 1981 to February 1982, 87 individuals (ages two months to 74 years) in the Seattle, WA, area developed the clinical symptoms of yersiniosis. Illness was related to consumption of commercial tofu (soybean curd) contaminated with Yersinia enterocolitica. The six Y. enterocolitica strains recovered from the hospitalized patients indicated that two antigenically distinct strains, 0:8 and 0:Tacoma, were involved. At the manufacturing site of the incriminated tofu, 112 Y. enterocolitica strains were recovered, of which two were serotype 0:8. The reactions of these strains were similar to those of clinical 0:8 strains in biochemical tests and in eight virulence factor tests. The LD50 for suckling mice was identical for all strains which killed mice. Although the causative organism(s) was not recovered from other samples of packaged tofu, our findings incriminated water used in the processing of tofu as the source of infection. The source of the second Y. enterocolitica strain (0:Tacoma) in this outbreak was not identified.