Purpose: The objectives of this study were to develop a quantitative microbial risk assessment model to evaluate the public health risks associated with consumption of fresh-cut lettuce contaminated with Escherichia coli O157:H7 in the U.S., and to evaluate the impact of potential intervention strategies on public health risks.
Methods: The supply chain of fresh-cut lettuce was modeled from in field production until consumption at home. Using @RISK software a simulation model was developed for exposure and health outcome assessment. The developed model was simulated using Latin Hypercube Sampling for 100,000 iterations to estimate the number of illnesses due to consumption of fresh-cut lettuce in the U.S.
Results: With a prevalence of 0.1% of incoming lettuce to the processing plants, the baseline model (with no inclusion of intervention strategies) predicted 76 cases per million people in the U.S. Among four different intervention strategies evaluated (consumer washing, irradiation, ultrasound and bacteriophages), spraying the lettuce with Escherichia coli O157:H7 specific lytic bacteriophages cocktail was the most effective in reducing the public health risks. Sensitivity analysis results indicated that washing with chlorine is the most important factor affecting the number of cases per year predicted.
Significance: The developed risk model can be used to characterize and estimate the microbiological risks associated with Escherichia coli O157:H7 in fresh-cut lettuce and to evaluate potential intervention strategies to mitigate such risks.