July 13, 2001 - Risk Management Action Plan for Foodborne Listeria Monocytogenes

The American Society for Microbiology (ASM) would like to comment on the draft Risk Assessment Document and Risk Management Action Plan for relative risk to public health from foodborne Listeria monocytogenes in ready-to-eat foods published January 19, 2001, in the Federal Register.

The ASM is the premier educational and scientific society dedicated to the advancement of microbiological research and its application for the common good. The Society represents more than 42,000 microbiologists, including scientists in academic, industrial and government institutions, working in a variety of areas, including medical, genomic, molecular, environmental and food microbiology, and public health.

The ASM commends the Food and Drug Administration (FDA) and the Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA) for undertaking a quantitative microbiological risk assessment of L. monocytogenes in selected categories of ready-to-eat foods to reduce the risk of foodborne listeriosis. The Society supports the concept of quantitative microbiological risk assessments of foods, when appropriately modeled, as a science-based approach to providing risk managers needed information for reducing human illness from foodborne pathogens.

The FDA/USDA risk assessment is designed to determine the risk of acquiring listeriosis from twenty different food groups. However, the assessment is based on a paucity of data within several of the food categories and fails to consider the differences in listerial growth rates among foods that were combined into specific categories. For example, only one study, which was based on growth of listeriae in orange juice serum, was used to determine the growth potential of L. monocytogenes for the entire fruit category. This is not an appropriate method of determining representative growth media for the many different types of fruit. Fruits vary widely in acidity, sugar content, and antilisterial properties, hence the growth rates of L. monocytogenes on different types of fruit (especially fresh cut) can be markedly different. For example, growth of L. monocytogenes on fresh-cut honeydew melon or cantaloupe of pH 6.0 to 6.5 would predictably be much greater than in orange juice serum at pH 5.0.

It is surprising that legume and vegetable sprouts, which have been identified as potentially hazardous because of their past association with several outbreaks of foodborne illness, were not given special attention. Pathogens like Salmonella, E. coli O157:H7, and L. monocytogenes can grow prolifically within sprouts during production. Failure to include meaningful survey data of the prevalence of L. monocytogenes in sprouts and data regarding the growth of listeriae in sprouts during production does not lend credence to the assessment. In fact, sprouts were included in the vegetable category and considered a low risk product based on data for other types of vegetables. Considering that an estimated 10% of the U.S. population consumes sprouts and that sprouts are considered to be a potentially high risk food, specific attention is warranted for this food group and it should be placed in a category of its own. Even grouping lettuce and cabbage in the same category is a gross oversimplification because studies indicate listeriae grows well in refrigerated cabbage but not as well in lettuce. An outbreak of listeriosis in Canada was associated with cole slaw made from contaminated cabbage, indicating the significance of cabbage as a vehicle of listeriosis. Yet the assessment classifies the vegetable category as low risk because many of the vegetables included in the database do not support prolific growth of L. monocytogenes. This is misleading and should be revisited by the FDA and USDA.

Similar concerns exist for the meat category. Deli meats have been oversimplified to include a wide variety of processed meats of which some, such as certain types of roast beef, may not support listerial growth, whereas others such as cooked poultry meat may serve as a medium for prolific growth of listeriae. As with the fruit and vegetable categories, the risk assessment inappropriately groups low and high-risk products together to maintain commodity categorization. The assessment should place greater emphasis on the growth of L. monocytogenes during refrigeration of problematic foods, such as cabbage, in relation to product storage life.

An additional concern regarding the L. monocytogenes risk assessment is that the ranking system used to "rate" the potential risk of acquiring listeriosis from different foods appears to be more precise and certain than it actually is. Based on the data provided, there appears to be more certainty in the numbers assigned at the high and low ends of the food categories than for those foods rated in the middle of the rankings, which are of "uncertain" risk. In place of a numeric rating system, the assessment should place food groups of questionable ranking in an "uncertain" category and thus eliminate misleading definitions of risk. Foods that have been determined to be of a high likelihood of transmitting listeriosis could be identified as "high" risk and those foods determined to be of minimal risk could be classified as "low" risk.

The ASM appreciates the initiative of FDA and USDA in undertaking this very complex and needed risk assessment of L. monocytogenes in ready-to-eat foods. However, we have concerns with the categorization and ranking system in the assessment. Foods with disparate potential for growth of L. monocytogenes have been inappropriately grouped together in the interest of providing a minimal number of broad food categories. This is an oversimplification for identifying high or low risk food types. Furthermore, the assessment identifies food groups with precise numerical rankings, disregarding certainty and degree of relative risk. These are serious deficiencies that weaken the integrity and usefulness of the risk assessment. Although we have described problems with the assessment, we support the goals of the assessment and encourage the FDA and USDA to continue to improve the model for conducting a qualitative risk assessment of L. monocytogenes in ready-to-eat foods.

The ASM is pleased to have the opportunity to provide comments in response to the draft risk assessment for L. monocytogenes and hopes that these comments and recommendations are of assistance to FDA and FSIS.

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