A POINT-SOURCE FOODBORNE LISTERIOSIS OUTBREAK - DOCUMENTED INCUBATIONPERIOD AND POSSIBLE MILD ILLNESS

Listeria bacteremia occurred in 2 pregnant women whose only common exp osure was attendance at a party. The incubation period, the possibilit y of mild disease due to Listeria infection, and foods associated with risk of disease were evaluated. Ten (28%) of 36 party attenders met a case definition, which included isolation of Listeria monocytogenes f rom blood or stool or two of the following: fever, musculoskeletal sym ptoms, nausea, vomiting, diarrhea. One of 25 stool cultures was positi ve. The 2 blood isolates and 1 stool isolate were serotype 4b and iden tical by enzyme typing. The incubation periods for illness in the 2 pr egnant women were 19 and 23 days. Consumption of large amounts of shri mp, nonalcoholic beverages, Camembert cheese, and cauliflower was sign ificantly associated with illness. Eating shrimp remained a significan t risk factor for illness after controlling for consumption of other f oods. This study suggests a milder illness may exist in healthy person s who consume foods contaminated with L. monocytogenes and demonstrate s a prolonged incubation period for disease.