Effects of at-home-preparation on the risk of foodborne illness in Japan: Analysis of quantitative microbial risk assessment of Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Campylobacter jejuni in lettuce salad made at home

This study assessed the influence of preparing iceberg lettuce salads at home on the risk of Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Campylobacter jejuni by conducting quantitative microbial risk assessments (QMRAs¹) for distribution, retail, domestic storage, and cross-contamination. The QMRA simulated pathogen behaviors in lettuce and meat from-farm-to-fork environments. Order of food preparation, hand washing, and lettuce washing were assessed in domestic lettuce salad and raw meat processes. Scenario and sensitivity analyses were performed to compare the importance of the process factors. QMRA simulation revealed that factors related to initial contamination and at-home preparation of foods were more critical than those related to the time-temperature environment during distributions and storages. The risk of L. monocytogenes infection decreased only 1 % even in the absence of cross-contamination. Similarly, the risk of C. jejuni hardly decreased (0.91-fold) even in the absence of lettuce contamination. When the lettuce was not washed, the risk of L. monocytogenes was relatively higher (1.92-fold) than that of other pathogens (E. coli O157:H7,1.44-fold; S. Typhimurium, 1.38-fold; and C. jejuni, 1.36-fold). The risk of E. coli O157:H7 (2.60-fold), S. Typhimurium (2.18-fold), and C. jejuni (2.67-fold) increased when hands were not washed before lettuce preparation, whereas the risk of L. monocytogenes did not increase (1.07-fold). The importance of avoiding cross-contamination through appropriate order of food preparation and hand washing in lettuce salad preparation were quantitatively demonstrated in the present study, which provide essential information for food safety education at home.