A Point-Source Foodborne Listeriosis Outbreak: Documented Incubation Period And Possible Mild Illness

TLDR

A Listeria bacteremia outbreak linked to a single party attendance was identified in two pregnant women. The study aimed to determine the incubation period, assess the possibility of mild Listeria disease, and identify foods associated with infection risk. Among 36 attendees, 10 met case criteria, with serotype 4b isolates, incubation periods of 19–23 days, and shrimp consumption emerging as a significant risk factor, indicating that mild illness may occur in healthy individuals and that Listeria can have a prolonged incubation.

Abstract

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.