Purpose: The goal of this project was to develop a simulation-based decision support system to assist public health epidemiologists in the control of outbreaks of foodborne pathogens. When an outbreak is suspected, a case control study is often performed to identify culprit foods types and consumption sites. We designed and analyzed simulated foodborne outbreaks to examine factors that influence capacity to determine their sources.
Method: We developed an agent-based model of foodborne disease to include details that maximized relevance to public health investigation. Individual agents representing community residents consumed meals consisting of different types of food at home or at restaurants. Food was either contaminated in the supply chain or during meal preparation via infected food preparers. Meal contamination was influenced by kitchen practices and preparer hygiene. A community of 100,000 individuals, 22,000 households, and 500 restaurants was modeled. Epidemiologic characteristics of the infection were calibrated to fit enterohemorrhagic E. coli. Synthetic data outputs consisted of individual-level exposures and disease status, to simulate the data collected during the course of an outbreak investigation. Case-control analyses were constructed to measure disease-exposure associations to assess whether the primary source of the outbreak was detectable. Two outbreak scenarios were tested across different levels of secondary transmission: 1) focused contamination of one food type in a few restaurants; 2) lower contamination of one food type across 10% of all homes and restaurants. Food contamination from infected preparers was varied in the sensitivity analysis. Each simulation was run for 90 days. The outbreak was injected into the community at day 60; 100 runs were executed for each scenario.
Result: At baseline, 5 - 10 cases occurred per month. The size of the outbreak ranged between 25 and 500 depending on stochastic variability and the level of transmissibility. Impairment of detection of a specific source restaurant was observed in scenario one when transmissibility was high and in scenario two at all levels of transmissibility. Impairment of detection of a specific source food was observed when transmissibility was high.
Conclusion: These results highlight challenges in detection of different types of sources of foodborne outbreaks. The origin of the outbreak may be obscured, depending on factors such as transmissibility, diversity of contaminated foods, and number of eating establishments involved.
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