A NATIONAL OUTBREAK OF SALMONELLA-ENTERITIDIS INFECTIONS FROM ICE-CREAM

Background. In September 1994, the Minnesota Department of Health dete cted an increase in the number of reports of Salmonella enteritidis in fections. After a case-control study implicated a nationally distribut ed brand of ice cream (Schwan's) in the outbreak, the product was reca lled and further epidemiologic and microbiologic investigations were c onducted. Methods. We defined an outbreak-associated case of S. enteri tidis infection as one in which S. enteritidis was cultured from a per son who became ill in September or October 1994. We established nation al surveillance and surveyed customers of the implicated manufacturer, The steps involved in the manufacture of ice cream associated with ca ses of S. enteritidis infection were compared with those of products n ot known to be associated with infection matched for the date of manuf acture. Cultures for bacteria were obtained from ice cream samples, th e ice cream plant, and tanker trailers that had transported the ice cr eam base (premix) to the plant. Results. estimate that S. enteritidis gastroenteritis developed in 224,000 persons in the United States afte r they ate Schwan's ice cream. The attack rate for consumers was 6.6 p ercent. Ice cream associated with infection contained a higher percent age of premix that had been transported by tanker trailers that had ca rried nonpasteurized eggs immediately before (P = 0.02). S. enteritidi s was isolated from 8 of 266 ice cream products (3 percent), but not f rom environmental samples obtained from the ice cream plant (n = 157) or tanker trailers (n = 204). Conclusions. This nationwide outbreak of salmonellosis was most likely the result of contamination of pasteuri zed ice cream premix during transport in tanker trailers that had prev iously carried nonpasteurized liquid eggs containing S. enteritidis. T o prevent further outbreaks, food products not destined for repasteuri zation should be transported in dedicated containers.