An Insidious Nosocomial Outbreak Due toSalmonella enteritidis

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Abstract
Objectives:: To investigate an increase in the number ofSalmonella enteritidisisolates detected in a large hospital to ascertain whether it was due to a nosocomial source, to identify the mechanisms of transmission, and to institute effective control measures to prevent future episodes.Design:: Observational study, survey of all microbiological samples positive forS. enteritidisdetected in the hospital, outbreak investigation, and review of the literature.Setting:: A tertiary-care teaching hospital for adults in Barcelona, Spain.Results:: During a 7-month period from May to November 1998, we identified 22 inpatients withS. enteritidisinfection for whom nosocomial acquisition was strongly suspected. The attack rate was 0.138 per 1,000 patient-days. All affected patients were immunosuppressed and overall mortality was 41% (9 of 22). A sample of a meal cooked in the kitchen was culture positive forS. enteritidis.All isolates shared the same antibiotic susceptibility pattern and all except one shared the same pulsed-field gel electrophoresis (PFGE) pattern, but PFGE could not differentiate between outbreak-related and control strains. After compliance with kitchen hygiene procedures was emphasized and cleansing was intensified, no more cases were detected.Conclusions:: Apparently, sporadic cases ofS. enteritidismay be part of an outbreak with a low attack rate. A small but persistent inoculum affecting only individuals with special predisposition forSalmonellainfection might account for this. Suspicion should be raised in hospitals and institutions with a highly susceptible population.