July 2, 1999 - Risk Assessment of the Public Health Impact of Foodborne Listeria Monocytogenes

Docket No. 99N-1076; Federal Register, Vol. 64: 24661-24663; Risk Assessment of the Public Health Impact of Foodborne Listeria monocytogenes; Request for Comments and for Scientific Data and Information."

In response to the notice published May 7, 1999, in the Federal Register, the ASM would like to comment on the planned risk assessment of the public health impact of foodborne Listeria monocytogenes.

The American Society for Microbiology (ASM) is the premier educational, professional, and scientific society dedicated to the promotion of the microbiological sciences and their applications for the common good. The Society represents more than 42,000 microbiologists, including scientists and science administrators in academic, industry and government institutions working in a variety of areas, including applied and environmental microbiology, food science, and medical microbiology.

Listeriosis is a relatively rare but serious illness. Based on the most current CDC data, the incidence of listeriosis in the U.S. is about 0.5 cases per 100,000 population. However, the rate of hospitalization is about 88% cases, the highest of all foodborne illnesses reported in CDC's Foodborne Diseases Active Surveillance Network (FoodNet). Furthermore, CDC data shows that about 20% persons infected with L. monocytogenes die. This is the highest case fatality rate of all foodborne illnesses reported in FoodNet.

The incidence of L. monocytogenes in the food supply is widespread with the organism being found in a variety of foods including soft-ripened, cured and other cheeses, raw vegetables, raw and cooked meats and poultry, seafood, fluid milk, and fermented meats. The organism can be naturally present in raw foods or it can be present in cooked, processed foods as a result of recontamination. Furthermore, research has shown that L. monocytogenes, even when initially present at low numbers, in certain foods, can grow to high levels over storage at refrigerated temperatures. Other foods may allow for the survival of the organism but will not permit its growth to high levels, while in other foods, the organism will die-off over time. The formulation of the food is a critical consideration and must be taken into account relative to how the organism will behave over product shelf-life.

While little is known regarding the infective dose for L. monocytogenes in humans, anecdotal evidence suggests that the ingestion of low levels of the organism (e.g. U>< 100/gram) does not represent a general public health hazard. In fact, other countries, including major trading partners of the U.S., such as Canada and Denmark will allow for low levels of L. monocytogenes in certain foods which will not allow for its growth. This accommodation for low levels of L. monocytogenes in these classes of foods reflects the recognition by these countries that this organism is widespread in the food supply and difficult to completely eradicate.

Considering this background, ASM lauds the FDA and USDA/FSIS for their plans to initiate a joint, scientific-based assessment of the risk of foodborne L. monocytogenes to the American public. ASM strongly endorses the goal of this risk assessment which is to provide FDA and FSIS with the information needed to review current programs relating to the regulation of L. monocytogenes contamination in foods to ensure that such programs provide maximum public health protection. An additional benefit of this approach is that it brings focus to those foods which represent a real threat to public health if not properly managed.

The approach to the risk assessment plan in the May 7, 1999 Federal Register notice is to analyze three types of information:

  1. The epidemiology of foodborne listeriosis
  2. The level of L. monocytogenes contamination of foods and their consumption level
  3. The human health consequences of such exposure (i.e. a dose-response analysis).

Information is needed on all three of these areas in order to perform a meaningful, scientific-based risk assessment. ASM offers the following specific comments for consideration on the proposed risk assessment plan:

  1. A thorough analysis of the epidemiology of foodborne listeriosis is warranted in order to prioritize those foods which have been associated with disease in humans. It is appropriate to focus risk assessment efforts on those foods which represent an increased risk to the American consumer based on direct clinical or indirect epidemiological evidence.
  2. ASM concurs that the initial focus of the risk assessment should be on those ready-to-eat foods which are intended for consumption without additional heating. However, the risk assessment should not be limited solely to foods in this category. Foods known or suspected to contain L. monocytogenes that have not been implicated in illness should also be considered in order to obtain a more complete database on overall exposure to the organism. A critical component of a meaningful quantitative risk assessment is knowing the level of L. monocytogenes present in foods at the time of consumption. Quantitative data on the presence of L. monocytogenes in foods may be difficult to obtain because of the "zero tolerance" position of U.S. regulatory agencies for L. monocytogenes in ready-to-eat foods. Most available data on the incidence of L. monocytogenes in foods is qualitative, not quantitative. Hence, the Agency's request for quantitative data, even under "blinded" conditions may not initially yield sufficient data for a meaningful quantitative risk assessment. The Agency should continue to urge scientists in industry and academe to generate quantitative data, and submit it to FDA in a "blinded" format. Agency funding should be provided to support comprehensive quantitative surveys where they would contribute useful data for completion of the risk assessment. One such initiative, for example, is the current study planned by the National Food Processors Association's Research Foundation which will examine quantitative levels of L. monocytogenes in ready-to-eat foods in the CDC's FoodNet catchment locations. Another important consideration is the ability of foods to support the growth of L. monocytogenes to high levels. The levels of L. monocytogenes in a food at the time of enumeration may, very well, be significantly different than the levels at the time of consumption. Factors such as age of product, temperature fluctuation, and consumer handling and preparation can have a major influence on the number of listeriae in a food at the time of consumption. A meaningful risk assessment should include these parameters in the evaluation. Use of consumption databases is a logical approach for exposure assessment. However, the two government databases to be used (CSF II 94-96 and NHANES III) do not include residents of institutions such as nursing homes and hospitals. Since these settings house a much higher than normal population of immunocompromised individuals who are most susceptible to listeric infection, some attempt should be made to understand food consumption patterns and exposure to L. monocytogenes through food in these settings. Input from the healthcare and nursing care sectors may be needed to ascertain this information.
  3. The third critical component of the risk assessment plan is an evaluation of the dose-response relationship which will describe the health effects from consuming specific levels of L. monocytogenes in food. However, this component is difficult to determine because studies on humans are not possible. Hence, ASM endorses the approach to use epidemiologic, animal, or in vitro studies wherever possible and scientifically defensible. In particular, the approach to use animal models as a surrogate for human studies should be supported, if they hold the best promise for generating a meaningful dose-response relationship.

The ASM is pleased to have the opportunity to provide comments in response to the notice and request for comments and scientific data and information on the Risk Assessment of the Public Health Impact of Foodborne L. monocytogenes. ASM believes that this is the best approach for identifying foods and food processing and preparation practices of greatest risk to enable industry and government to better focus their resources in areas that will have the greatest impact on reducing the risk of listeriosis to the American public.