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Society For Risk Analysis Annual Meeting 2009

Risk Analysis: The Evolution of a Science

Session Schedule & Abstracts

* Disclaimer: All presentations represent the views of the authors, and not the organizations that support their research. Please apply the standard disclaimer that any opinions, findings, and conclusions or recommendations in abstracts, posters, and presentations at the meeting are those of the authors and do not necessarily reflect the views of any other organization or agency. Meeting attendees and authors should be aware that this disclaimer is intended to apply to all abstracts contained in this document. Authors who wish to emphasize this disclaimer should do so in their presentation or poster. In an effort to make the abstracts as concise as possible and easy for meeting participants to read, the abstracts have been formatted such that they exclude references to papers, affiliations, and/or funding sources. Authors who wish to provide attendees with this information should do so in their presentation or poster.

Common abbreviations

What's New in Risk Assessment for Listeria Monocytogenes?

Room: Homeland   1:30-3:00 PM

Chair(s): Regis Pouillot

T3-F.1  13:30  A joint FDA/Health Canada risk assessment: Listeria monocytogenes in soft-ripened cheese . Gendel SM*, Pouillot R, Murray C; FDA, Center for Food Safety and Applied Nutrition, College Park, Maryland

Abstract: The United States and Canada continue to experience sporadic illnesses and outbreaks of listeriosis associated with the consumption of cheese. The 2003 FDA/USDA risk assessment for Listeria monocytoges in ready to eat foods suggested that there may be as much as a 40-fold increased risk for listeriosis from consumption of soft and soft-ripened cheeses made from unpasteurized milk as compared to cheese made from pasteurized milk. Both the FDA Center for Food Safety and Applied Nutrition and the Health Canada (HC) Food Directorate continue to evaluate the safety of soft cheese, particularly soft cheese made from unpasteurized milk. To support this evaluation, FDA and HC are jointly developing a quantitative microbial risk assessment to assess the public health impact of L. monocytogenes in soft-ripened cheese, particularly Brie and Camembert. This risk assessment extends previous work by focusing on the source(s) of L. monocytogenes in the production pathway, the effects of individual manufacturing and processing steps on the presence and level of L. monocytogenes, and the effectiveness of various intervention strategies for reducing or controlling L. monocytogenes. The risk assessment team has developed a product pathway model that includes a description of the cheese production process from the collection of milk on the farm to at-home storage of the finished cheese. The exposure assessment also considers consumption patterns for several subpopulations. The hazard characterization component of the model includes descriptions of relative susceptibilities in the general population and three susceptible sub-populations (pregnant woman, the immunocompromised, and the ageing population). The primary output of the model, the risk characterization, is a description of risk expressed as the probability of illness per serving. The model permits evaluation of changes in the predicted risk associated with modifications of existing manufacturing processes, such as the use of new or additional interventions, and changes in consumer handling practices.

T3-F.2  13:50  A comparative risk assessment for Listeria monocytogenes in ready-to-eat meat and poultry products. Akingbade DA*, Gallagher D, LaBarre D, Kause J; Risk Assessment Division, Office of Public Health Science, Food Safety and Inspection Service, Washington DC (1, 3, 4), Civil and Environmental Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA (2)

Abstract: The comparative risk of Listeria monocytogenes (L. monocytogenes) in retail sliced versus prepackaged deli meats was evaluated using a modified version of the 2003 FDA-FSIS risk assessment model. The updated risk assessment model considered slicing location as well as the use of growth inhibitors in estimating the number of annual deaths from listeriosis for three age groups; neonatal, intermediate, and elderly. L. monocytogenes prevalence data for retail-sliced and prepackaged deli meats was fit to probability distributions which served as the inputs for the FDA-FSIS model. The model estimated the total number of deaths for retail-sliced and prepackaged deli meats as well as for product with and without growth inhibitors. The per annum comparative risk ratio for the number of deaths from retail-sliced versus prepackaged deli meats was found to be 4.89 and the per serving comparative risk ratio was 4.27. There was a significant interaction between the use of growth inhibitors and slicing location. Almost 70% of listeriosis deaths associated with deli meats occurred from retail-sliced product that did not use a growth inhibitor. A sensitivity analysis assessing the effect of the model's consumer storage time and shelf life assumptions found that even if retail-sliced deli meats were stored for a quarter of the time prepackaged deli meats were stored, retail sliced product is 1.7 times more likely to result in death from listeriosis, whereas the shelf life assumption had little effect on the comparative risk ratio. The findings suggested that post-processing cross contamination is occurring among retail-sliced deli meats. Further preventive measures focused at the retail level may help reduce the risk of listeriosis.

T3-F.3  14:10  Modeling Listeria monocytogenes cross-contamination dynamics within a quantitative risk assessment. Ivanek R*, Grohn YT, Wiedmann M, Wells MT; 1 Texas A&M university; 2,3 and 4 Cornell university

Abstract: Listeriosis is a food-borne disease caused by the bacteria Listeria monocytogenes. The food industry and government agencies devote considerable resources reducing contamination of ready-to-eat foods with L. monocytogenes. Because inactivation treatments can effectively eliminate L. monocytogenes present on raw materials, for pre-packaged foods, post processing cross-contamination from the processing plant environment appears to be responsible for most L. monocytogenes food contamination events. To be able to better prevent L. monocytogenes contamination and thus reduce the risk of human exposure to L. monocytogenes, an improved understanding of cross-contamination pathways, including how to model them in a quantitative risk assessment, is critical. Therefore, a plant specific mathematical model of L. monocytogenes cross-contamination was developed, which described the transmission of L. monocytogenes contamination among food, food contact surfaces, employees’ gloves and the environment. A smoked fish processing plant was used as a model system. The model estimated that 12.3% (5th and 95th percentile, 2.2% and 22.5%, respectively) of food products in a lot are likely to be contaminated with L. monocytogenes. Sensitivity analysis identified that the most significant input parameters are the frequency of contacts that employees’ gloves make with food and food contact surfaces, and the frequency of changing gloves. Scenario analysis indicated that the greatest reduction of the within lot prevalence of contaminated food products can be achieved if the raw material entering the plant and the plant environment (which employees touch with their hands) are completely free of contamination. Zero contamination of food products in a lot was possible but very rare. This model could be used in a risk assessment to quantify the potential public health benefits of in-plant control strategies to reduce cross-contamination.

T3-F.4  14:30  Validating models for the growth/no-growth boundary for Listeria monocytogenes in mis-formulated ready-to-eat foods. Schaffner DW*, Schaffner KM, Liu B, Bruins HB; Rutgers University

Abstract: There is interest in determining the margin of safety provided by the current formulations of various food products that might support the growth of Listeria monocytogenes. Understanding the susceptibility of such product to misformulation can be important to risk assessment and food safety. One example of such a formulated food product is the “pocket sandwich” developed by the US Army. These products are considered stable with respect to growth of L. monocytogenes because their water activity is either less than 0.90, or the water activity is less than 0.95 and the pH is less than 5.5. A challenge study with various product formulation omissions was used to simulate accidental mis-formulations that could raise either the pH and/or water activity. A total of nine variants of two sandwich products (Honey Barbeque and Bacon Cheddar) variants were made, including control for each. Samples of each of these variants were analyzed for pH and Aw. All product variants were inoculated with a seven strain L. monocytogenes cocktail. Samples were incubated at 25°C for 360 days. Microbial testing was performed at regular time intervals during this period. Listeria monocytogenes appears to gradually die off in all formulations of BBQ Beef and Bacon Cheddar sandwiches. A decline from 5 log CFU to 3 log CFU was observed over a 6 month period or about 0.33 log CFU per month. Therefore, L. monocytogenes growth in pocket sandwiches (even if incorrectly formulated) appears very unlikely. The results from this study also validate a model previously developed by Koutsoumanis et al (2004) on growth limits of Listeria monocytogenes as affected by temperature, pH and water activity when grown in suspension or on a solid surface. This approach (model validation against deliberately mis-formulated products) might prove useful in expanding the scope of current L. monocytogenes risk assessments.

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