METHODS: MCHD/CDS conducted a cohort study to assess the cause of illness. Questionnaires were developed in Google Forms and emailed to 492 conference registrants. The confirmed case definition included persons who ate conference food and had laboratory confirmed S. Typhimurium with matching PFGE pattern. Probable cases included contemporaneous cases without laboratory confirmation and experiencing vomiting and/or 3+ episodes of loose stool in a 24-hour period. Data from the questionnaires were analyzed using SAS v9.4 software. We calculated relative attack rates (RR) with confidence intervals (CI) for meals and foods served during the conference.
RESULTS: Our cohort included 223 questionnaire respondents among the 492 people who registered for the conference. Respondents came from 5 countries and, within the United States, 16 states. We identified 12 confirmed cases and 41 probable cases. Conference attendees who consumed lunch on Thursday were more likely to become ill compared to attendees who didn’t consume lunch on Thursday (RR 10.12 [95% CI 3.78-27.10]). People who ate the vegetable stir-fry or curry at any time were 5-7 times more likely to develop illness then conference attendees who didn’t eat these dishes; in considering only confirmed cases, the risk was stronger (11-20). The EH investigation found that the two foods identified in the epidemiologic study were mixed and improperly reheated inside a motor home that wasn’t approved for catering.