Yersinia frederiksenii infection and colonization in hospital staff

A diagnosis of gastrointestinal infection with Yersinia frederiksenii was made in a 24-year-old female hospital doctor, resident in hospital. An additional three of nine medical residents screened were found to be faecal carriers of Y. frederiksenii. The latter three residents denied any gastrointestinal symptoms. Screening of 25 resident nurses and 25 in-patients for carriage of Y. frederiksenii was negative. Initial investigation revealed that the medical residents frequently drank unpasteurized milk, which was supplied on the understanding that it would be used for cooking only. Counts of > 10(8) cfu l-1 were obtained from unpasteurized milk samples, including 24 species of Gram-negative bacilli. Yersinia spp. were not isolated. Residents also drank water from the cold taps in the bedrooms; this water was supplied by a holding tank on the hospital roof. Subsequent investigations revealed that three of the 21 holding tanks supplying stored water to the hospital were not covered. Y. enterocolitica was isolated from the uncovered water tank supplying the medical residence.