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Background In September 1994, the Minnesota Department of Health detected an increase in the number of reports of Salmonella enteritidis infections. After a case–control study implicated a nationally distributed brand of ice cream (Schwan's) in the outbreak, the product was recalled and further epidemiologic and microbiologic investigations were conducted.
Methods We defined an outbreak-associated case of S. enteritidis infection as one in which S. enteritidis was cultured from a person who became ill in September or October 1994. We established national surveillance and surveyed customers of the implicated manufacturer. The steps involved in the manufacture of ice cream associated with cases of S. enteritidis infection were compared with those of products not known to be associated with infection matched for the date of manufacture. Cultures for bacteria were obtained from ice cream samples, the ice cream plant, and tanker trailers that had transported the ice cream base (premix) to the plant.
Results We estimate that S. enteritidis gastroenteritis developed in 224,000 persons in the United States after they ate Schwan's ice cream. The attack rate for consumers was 6.6 percent. Ice cream associated with infection contained a higher percentage of premix that had been transported by tanker trailers that had carried nonpasteurized eggs immediately before (P = 0.02). S. enteritidis was isolated from 8 of 266 ice cream products (3 percent), but not from 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 pasteurized ice cream premix during transport in tanker trailers that had previously carried nonpasteurized liquid eggs containing S. enteritidis. To prevent further outbreaks, food products not destined for repasteurization should be transported in dedicated containers.
Source Information
From the Acute Disease Epidemiology Section (T.W.H., C.W.H., K.E.W., K.L.M., M.T.O.), the Public Health Laboratory (J.M.B.-W.), and the Executive Office (M.E.M.), Minnesota Department of Health, Minneapolis; the Division of Field Epidemiology and Epidemic Intelligence Service (T.W.H.), and the Foodborne and Diarrheal Diseases Branch, National Center for Infectious Diseases (L.S.), Centers for Disease Control and Prevention, Atlanta; the Food and Drug Administration, Minneapolis (J.F.); the Division of Dairy and Food Inspection, Minnesota Department of Agriculture, St. Paul (W.W.C.); and Disease Prevention and Control, Olmsted County Health Department, Rochester, Minn. (L.M.E.).
Address reprint requests to Dr. Osterholm at the Acute Disease Epidemiology Section, Minnesota Department of Health, 717 Delaware St., SE, P.O. Box 9441, Minneapolis MN 55440-9441.
Related Letters:
An Outbreak of Salmonella Infection from Ice Cream
O'Ryan M., Djuretic T., Wall P. G., Nichols G., Hennessy T. W., Slutsker L., Hedberg C. W., MacDonald K. L., Osterholm M. T.
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Full Text
N Engl J Med 1996;
335:824-825, Sep 12, 1996.
Correspondence
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