Leveraging risk assessment for foodborne outbreak investigations: The Quantitative Risk Assessment‐Epidemic Curve Prediction Model

Abstract

Root cause analysis can be used in foodborne illness outbreak investigations to determine the underlying causes of an outbreak and to help identify actions that could be taken to prevent future outbreaks. We developed a new tool, the Quantitative Risk Assessment-Epidemic Curve Prediction Model (QRA-EC), to assist with these goals and applied it to a case study to investigate and illustrate the utility of leveraging quantitative risk assessment to provide unique insights for foodborne illness outbreak root cause analysis. We used a 2019 Salmonella outbreak linked to melons as a case study to demonstrate the utility of this model (Centers for Disease Control and Prevention [CDC], 2019). The model was used to evaluate the impact of various root cause hypotheses (representing different contamination sources and food safety system failures in the melon supply chain) on the predicted number and timeline of illnesses. The predicted number of illnesses varied by contamination source and was strongly impacted by the prevalence and level of Salmonella contamination on the surface/inside of whole melons and inside contamination niches on equipment surfaces. The timeline of illnesses was most strongly impacted by equipment sanitation efficacy for contamination niches. Evaluations of a wide range of scenarios representing various potential root causes enabled us to identify which hypotheses, were likely to result in an outbreak of similar size and illness timeline to the 2019 Salmonella melon outbreak. The QRA-EC framework can be adapted to accommodate any food-pathogen pairs to provide insights for foodborne outbreak investigations.

Quantitative risk assessment‐epidemic curve prediction model for leafy green outbreak investigation

“…The observed differences in the impact of equipment sanitation efficacy between STEC O157-lettuce outbreak and Salmonella-melon outbreak are likely attributable to the difference in pathogen transfer rate from processing equipment surfaces. Compared to transfer rates from different equipment surfaces to melon cuts (Jensen et al, 2013;Mokhtari et al (2022b), transfer rates in our STEC-lettuce model (based on studies by Buchholz et al, 2012aBuchholz et al, , 2012bBuchholz et al, , 2014 were generally smaller, indicating a smaller number of pathogens were transferred to lettuce cuts upon contact with contaminated equipment compared to melons cuts. Jensen et al (2013) reported markedly less transfer of bacteria from common food contact surfaces to lettuce cuts compared to transfer of bacteria to cut melons.…”

“…Potential pathogen transfers during equipment sanitation practices were modeled following the approach described in Mokhtari et al. (2022b). Briefly, sanitation of equipment surfaces, including shredder, flume tank, conveyor belts, shaker table, centrifuge, and knives used by food handlers, was explicitly modeled by considering sanitation frequency and sanitation efficiency.…”

“…For whole lettuce, pathogen reduction achieved during consumer washing at home before consumption was also modeled. We further followed the approached described in Mokhtari et al (2022b) to estimate the number and timeline of illnesses (epidemic curve) due to consumption of contaminated fresh-cut or whole lettuce. The model framework is designed to be flexible and can be easily adapted for lettuce consumed at different settings (e.g., food service facility or restaurant) and can be accommodated for different leafy green commodities.…”

“…Previously, FDA developed a novel quantitative risk assessment‐epidemic curve prediction model (QRA‐EC) that extended traditional QRA to include epidemic curve predictions for foodborne illness outbreaks (Mokhtari et al., 2022b). The QRA‐EC approach can assist foodborne outbreak investigations through quantitative evaluations of potential root cause hypotheses (Mokhtari et al., 2022b).…”

“…Previously, FDA developed a novel quantitative risk assessment‐epidemic curve prediction model (QRA‐EC) that extended traditional QRA to include epidemic curve predictions for foodborne illness outbreaks (Mokhtari et al., 2022b). The QRA‐EC approach can assist foodborne outbreak investigations through quantitative evaluations of potential root cause hypotheses (Mokhtari et al., 2022b). Given the flexibility of the QRA‐EC approach, we tailored it for leafy greens to provide more nuanced risk estimates with epidemic curve predictions and new insights for outbreak investigations.…”