Risk ranking of microbiological hazards Salmonella spp. and Shiga toxin-producing E. coli (STEC) on strawberry, butterhead lettuce and fresh herbs

Risk ranking is a useful tool to set priorities in controlling or monitoring risks. A comparative retail to fork exposure assessment model was built to show the effect of storage mode, period and washing practices by Belgian and Spanish consumers on the concentration of Salmonella and E. coli O157 on basil, strawberries and butterhead lettuce. Taking the measured prevalence of the pathogens into account, a risk ranking is made aimed at comparing pathogens, commodities or regions within Europe. Data relating to the survival of Salmonella and E. coli O157 on basil, strawberries and butterhead lettuce and the prevalence of both pathogens Salmonella and STEC on these commodities were collected by lab experiments during the Veg-i-Trade project. In addition information about the removal of pathogens and E. coli from leafy greens and strawberries and consumer behavior relating to storage mode and period and washing practices (Belgian versus Spanish consumers) were collected from literature and by a consumer behavior questionnaire, respectively. The exposure assessment model was built in excel and run via Monte Carlo simulation in the add-in function @Risk (100 000 iterations). Simulating the model resulted in the concentration and prevalence after storage and washing at consumers house and a distribution of the number (and fraction) of contaminated portions in one year of consumption. The concentration of pathogens after storage was generally higher for the Belgian consumers compared to the Spanish consumers due to less frequent storage in refrigerator and shorter storage periods applied by Belgian consumers. A higher concentration on basil and butterhead lettuce was found compared to strawberries mainly due to the higher die off of the pathogens on strawberries compared to lettuce and basil. Taking washing practices in account similar ranking was obtained. In addition, a small decrease was noticed in prevalence, e.g. prevalence of Salmonella on strawberries at retail was max. 1,2% versus max. 0,8% after storage and washing practices for 95% of the Belgian consumers. By including consumption frequency, a distribution of the number of contaminated portions in one year was calculated. The highest number of contaminated portions was found in case of basil, followed by butterhead lettuce and strawberries, due to less die-off of the pathogens compared to strawberries, less storage in refrigerator, less washing and higher prevalence on basil. In addition, a higher number was found for basil in case of Salmonella compared to STEC, whereas both pathogens were comparable for strawberries and butterhead lettuce, due to difference in survival and prevalence of Salmonella and STEC on basil. A higher number of contaminated portions for strawberries was found when consumed by Belgian consumers, whereas for lettuce when consumed by Spanish consumers. This can be explained by the more frequent consumption of strawberries by Belgian consumers in contrast to the more frequent consumption of lettuce by the Spanish consumers in one year