Comparative simulation of Escherichia coli O157:H7 behaviour in packaged fresh-cut lettuce distributed in a typical Canadian supply chain in the summer and winter

The ability to predict the risk associated with Escherichia coli O157:H7 in packaged fresh-cut lettuce hinges on the availability of realistic times and temperatures encountered in commercial supply chains. We report here on temperature profiles measured in winter and summer months in a retail supply chain and their predicted impact on the fate of the pathogen in fresh-cut lettuce. Time and temperature data were recorded in individual packages within cases of lettuce in the bottom, middle and top layers of pallets distributed from a processing facility to retail storage. Measurements indicated there were occasional increases in temperature during either season and that temperatures were ≥5 °C for longer periods of time during the summer. A stochastic simulation model based on time and temperature distributions was constructed in @RISK™ to predict the fate of E. coli O157:H7. The output from the model demonstrated a range of possible outcomes for the time-temperature profiles measured in the commercial supply chain, ranging from slight growth to die-off. The outputs of the stochastic simulations were similar to analytical simulations based on actual times and temperatures experienced by product in the supply chain. The distributions presented in the current model could be incorporated in quantitative risk assessments to improve predictions about the prevalence and fate of E. coli O157:H7 in fresh-cut lettuce supply chains.