ROLE OF FOODS IN SPORADIC LISTERIOSIS .2. MICROBIOLOGIC AND EPIDEMIOLOGIC INVESTIGATION

Objective. - To evaluate the role of foods in sporadic listeriosis. Design. - Microbiologic survey of foods collected from refrigerators of patients with listeriosis identified through active laboratory-based surveillance. Patient and food Listeria monocytogenes isolates were subtyped to identify foods contaminated with the same strain of L monocytogenes that caused illness in the patient; samples of these foods were obtained from the retail source. Setting. - Multistate population-based study conducted between 1988 and 1990. Results. - Listeria monocytogenes grew from at least one food specimen in the refrigerators of 79 (64%) of 1 23 listeriosis patients; 11 % of more than 2000 food specimens collected in the study contained L monocytogenes. Twenty-six (33%) of 79 refrigerators with foods that grew L monocytogenes contained at least one food isolate of the same strain as that in the corresponding patient, a frequency much higher than would be expected by chance (P < .001). Multivariate analysis showed that of the food specimens that grew L monocytogenes, foods that were ready-to-eat, foods that grew L monocytogenes by a direct-plating method (a measure of the level of contamination), and foods that contained serotype 4b isolates were independently associated with an increased likelihood of containing the patient-matching strain. Conclusion. - We identified specific food and L monocytogenes isolate characteristics-ready-to-eat foods, foods containing higher concentrations of L monocytogenes, and foods containing serotype 4b-which were associated with disease-causing strains. These results can provide guidance to industry and regulatory agencies in developing strategies to prevent listeriosis.