A point-source foodborne listeriosis outbreak: documented incubation period and possible mild illness.

Listeria bacteremia occurred in 2 pregnant women whose only common exposure was attendance at a party. The incubation period, the possibility 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 from blood or stool or two of the following: fever, musculoskeletal symptoms, nausea, vomiting, diarrhea. One of 25 stool cultures was positive. The 2 blood isolates and 1 stool isolate were serotype 4b and identical by enzyme typing. The incubation periods for illness in the 2 pregnant women were 19 and 23 days. Consumption of large amounts of shrimp, nonalcoholic beverages, Camembert cheese, and cauliflower was significantly associated with illness. Eating shrimp remained a significant risk factor for illness after controlling for consumption of other foods. This study suggests a milder illness may exist in healthy persons who consume foods contaminated with L. monocytogenes and demonstrates a prolonged incubation period for disease.

Incidence of listeriosis in Connecticut.

In Connecticut, 92 cases of human listeriosis were reported to the Department of Health Services from 1984 to 1988. The annual incidence per million population ranged from 7.3 in 1984 to 4.2 in 1988. The average annual incidence was 5.6 per million population. Case rates were highest in those aged 70 years and older (15.8 per million). Cases included 12 pregnant women and 11 newborns. Bacterial meningitis was the primary diagnosis in 23 cases. Of the 49 isolates of Listeria monocytogenes that were serotyped, 21 (43%) were type 4, 24 (49%) were type 1, and 4 (8%) were nontypable.