| Objective:Listeria monocytogenes is a foodborne pathogen which can cause zoonotic disease. The pathogen could contaminate many types of foods, grow and reproduce in cold temperatures and lead to severe disease. In view of these characteristics of the bacteria, it caused widespread concern around the world. In this study, risk assessment model of Listeria monocytogenes in cooked meat products has been established. The semi-quantitative and quantitative assessment for Listeria monocytogenes in cooked meats in China have been conducted through the models, so as to provide national authorities with the scientific advice on risk management measures of controlling risk caused by Listeria monocytogenes.Method:1.Using Risk Ranger software to conduct the semi-quantitative assessment of Listeria monocytogenes in the cooked meats, vegetables salads and non-fermented soybean products.2.Using @Risk software to build a quantitative risk assessment model of Listeria monocytogenes in cooked meats at the retail-consumption step. The risk of listeriosis caused by consuming deli meats and packaged meats for different sub-population (0-4 years old,5-64 years old, and 65 years and older) was estimated respectively.3.Based on the dose-response relationship in quantitative risk assessment, the hypothetical scenario study was conducted in order to explore the impact of disease risk when setting different limits for Listeria monocytogenes in the cooked meats.4.Considering the risk assessment and hypothetical research results, propose the suggestions on risk management measures in China.Results:1.Relative risk for Listeria monocytogenes in cooked meats, vegetable salads and non-fermented soybean products is 61,52 and 57,respectively. Cooked meats/ Listeria monocytogenes pairs is at the highest risk, vegetable salad/Listeria monocytogenes pairs is at the lowest risk. When the relative risk increases 6,the absolute risk will increase 10 times.According to this conversion relationship, risk from cooked meats/Listeria monocytogenes is 10 times than risk from non-fermented soybean products and is 32 times than that of the vegetables salads.2.The model prediction results from quantitative risk assessment show that:estimated probability (median) of listeriosis incidence caused by deli meats per serving in young (0-4 years old),intermediate age (5-64 years old) and elderly (65 years and older) is 6.50×10-11,2.13×10-12 and 9.05×10-11,respectively;estimated number of cases (median) of listeriosis each year per million people for deli meats in young, intermediate age and elderly population is 5.53×10-3,1.72×10-4 and 7.57×10-3.For the package cooked meats, estimated probability (median) of listeriosis incidence in young, intermediate age, elderly and total population is 6.51×10-7,1.96×10-8 and 8.63×10-7; estimated number of cases (median) of listeriosis each year per million for corresponding sub-population is 55.9,1.69 and 71.2,respectively.3.Results of sensitivity analysis show that:contamination level at retail, serving size of cooked meat, storage time at home,storage temperature and EGR at 5℃are positive factors for the risk of listeriosis. For deli meats, contamination level at retail is the most relative factor. As for the packaged cooked meats, serving size will significantly affect the risk results.4.The impact of model resulted from storage temperature and time show that:when the deli meats are at the environment in the summer, concentration of Listeria monocytogenes will increase 5.75 log CFU/g (0.62 log CFU/g-17.531og CFU/g) after three days, probability of listeriosis incidence caused by deli meats per serving is 1.97×10-5 (1.02×10-10-1.24×10-2);if these deli meats are placed at environment in the spring and autumn, concentration of Listeria monocytogenes would increase 3.44 log CFU/g (0.36 log CFU/g-10.87 log CFU/g) after three days, probability of listeriosis incidence caused by deli meats per serving is 1.01×10-7 (4.20×10-11-6.43×10-3).By the comparison, results from the former (in the summer) are two orders of magnitude higher than the latter (in the spring and autumn). 5.Hypothetical research results for Listeria monocytogenes in cooked meat products show that:in the supposed non-threshold model, when the concentrations of Listeria monocytogenes in the cooked meats increase, the risk and expected number of cases of Listeriosis also increase.In theory, the effect of introducing into the food supply 10 0000 servings contaminated with Listeria monocytogenes at a level of 100 CFU/g could be compensated by removing from the food supply a single serving contaminated at level of 107 CFU/g.When the microbiological limit is set at<0.04 CFU/g and 100 CFU/g, the number of cases of listeriosis are the similar at the different defective percentage for packaged cooked meats.Conclusion:1.Using Risk Ranger software, we could obtain the results for risk ranking from cooked meat/Listeria monocytogenes, non-fermented soybean products/Listeria monocytogenes and vegetable salads/Listeria monocytogenes.The results show that cooked meat is a high risk food for listeriosis.2.Predicted results by using @ Risk software show that:the risk caused by packaged cooked meat products is higher than that of the deli meats. For deli meats and packaged cooked meat, young group and elder group are more susceptible than the intermediate-age group. Probability of foodborne illness caused by per serving food in these two groups is one order of magnitude higher than that of intermediate-age group. From the probability distribution of the evaluation results, it could obtain the conclusion that the consumer intake level of Listeria monocytogenes is proportional to the results of risk assessment. Therefore, we could believe that any strategic measures which could reduce exposure will reduce the risk.3.Result from study on storage temperature and time show that, regardless of the summer or fall, if the cooked meat left at room temperature, Listeria monocytogenes will show multiple rapid growths. Further evidences show that cold storage can significantly reduce growth and reproduction of Listeria monocytogenes.Influence of heat treatment on results of assessment model show, if heat treatment process at 70℃could last a few minutes, it will kill Listeria monocytogenes in cooked meats. It reminders that it is possible for consumers to effectively reduce or prevent the foodborne lisiteriosis by the heat treatment before consumption.4.Uncertainty analysis results of model from quantitative assessment reveal that, due to incomplete data and the detection limit of method, it may overestimate risk caused by consuming the packaged cooked meats in the assessment process.5.According to the risk assessment results, we suggest that risk managers should confirm the different risk management measures for deli meats and packaged cooked meats, with considering the different processing ways, consumption patterns and other characteristics.6.The suggestion on risk management measures for the listeria monocytogenes in the cooked meats are as follows:(1)Establish microbiological limits in finish products. We propose that standard of Listeria monocytogenes in packaged cooked meats is n= 5,c=0, m=0/25g and not to establish the standard for this pathogen in deli meats.(2) Revise and integrate the cooked meat-related code of practice; (3)Strengthen process control, and especially control listeria monocytogenes at the following steps (raw materials, processing, pre-packing, post-packing and pre-consumption); (4) Carry out education and training for supervision personnel, medical workers, food processors and consumers.Reduce the levels of listeria monocytogenes and ultimately protect consumer health by these management measures.
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