Evaluation of Potential Impacts of Free Chlorine during Washing of Fresh-Cut Leafy Greens on Escherichia coli O157:H7 Cross-Contamination and Risk of Illness.

Abstract

Addition of chlorine‐based antimicrobial substances to fresh‐cut leafy green wash water is done to minimize microbial cross‐contamination during processing. We developed the FDA Leafy Green Risk Assessment Model (FDA‐LGRAM) to quantify the impact of free chlorine concentration in wash water during fresh‐cut lettuce processing on the extent of water‐mediated cross‐contamination between shredded lettuce and the associated risk of illness due to exposure to Escherichia coli O157:H7. At different contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads, the model compared the predicted prevalence of contaminated fresh‐cut lettuce packages and the risk of illness per serving between: (1) a scenario where fresh‐cut lettuce was packaged without washing; and (2) scenarios involving washing fresh‐cut lettuce with different levels of free chlorine (0 ppm, 5 ppm, 10 ppm, 15 ppm, and 20 ppm) prior to packaging. Our results indicate that the free chlorine level in wash water has a substantial impact on the predicted prevalence of contaminated fresh‐cut lettuce packages and the risk of illness associated with E. coli O157:H7 in fresh‐cut lettuce. Results showed that the required level of free chlorine that can minimize water‐mediated cross‐contamination and reduce the corresponding risk of illness depended on contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads. Our model also indicated that the pathogen inactivation rate in wash water via free chlorine was a key model parameter that had a significant impact on the extent of cross‐contamination during washing and the predicted associated risk of illness.