FSIS Comparative Risk Assessment for Listeria monocytogenes in Ready-toeat Meat and Poultry Deli Meats Report

1

Executive Summary

FSIS Comparative Risk Assessment for Listeria monocytogenes in Ready-to-eat Meat and 

Poultry Deli Meats

May 2010

BACKGROUND

Listeria monocytogenes (L. monocytogenes) is an important foodborne pathogen, estimated to 

cause approximately 2,500 illnesses, 2,300 hospitalizations, and 500 deaths each year in the 

United States. In an effort to understand better the sources of foodborne L. monocytogenes 

infection, the Food and Drug Administration (FDA) and the Food Safety and Inspection Service 

(FSIS), working collaboratively, developed a quantitative microbial risk assessment for L. 

monocytogenes that compared the risk of listeriosis among twenty-three categories of ready-toeat (RTE) foods. The results of the risk assessment, completed in 2003, indicated that deli meats 

pose the greatest risk for listeriosis, accounting for approximately 1,600 illnesses per year.

Based on these findings, FDA and FSIS conducted a preliminary analysis using the 2003 FDAFSIS L. monocytogenes risk assessment model to evaluate the relative risk of illness from L. 

monocytogenes on deli meat sliced and packaged at federally-inspected processing 

establishments (prepackaged deli meat) compared to deli meat sliced at retail facilities. This risk 

assessment contained industry data for L. monocytogenes on retail deli meat from delicatessens 

in California and Maryland (Gombas et al., 2003). The results of this risk assessment indicated a 

high percentage of listeriosis cases related to deli meats were associated with those sliced at 

retail. Because these results, however, were based on limited retail L. monocytogenes 

contamination data for deli meats, FSIS sought to gather additional data specifically to examine 

the relative risk of illness from prepackaged deli meat compared to deli meat sliced at retail 

facilities more closely. Therefore, the U.S. Department of Agriculture, Agricultural Research 

Service funded the National Alliance for Food Safety and Security (NAFSS) – a consortium of 

twenty-five research universities – to conduct a four-state study in which prepackaged deli meat 

and deli meat sliced and packaged at retail were analyzed for the prevalence and level of L. 

monocytogenes (Draughon, 2006). 

METHODS

Data from the NAFSS study, described in Appendix A of this risk assessment report, were used 

as inputs to the deli meat exposure pathway developed by modifying the above-mentioned 2003 

FDA-FSIS L. monocytogenes risk assessment model for RTE foods. The pathway consists of 

four distinct stages. The Retail Stage determines the level of L. monocytogenes in prepackaged 

deli meats and in deli meats sliced at retail. The Growth Stage uses an exponential growth rate 

function to model growth of L. monocytogenes in deli meat between purchase at retail and 

consumption. The Consumption Stage uses information about deli meat serving sizes and the 

number of servings consumed to estimate consumer exposure to L. monocytogenes in deli meat. 

Lastly, by integrating the predicted exposure with a dose-response relationship, the Dose-
FSIS Comparative Risk Assessment for Listeria monocytogenes in Ready-toeat Meat and Poultry Deli Meats Report

2

Response Stage predicts the probability of death from consuming L. monocytogenes on deli 

meat. 

The modified model considered four categories of deli meats: retail-sliced versus prepackaged 

and with or without growth inhibitor. Consumer storage times were based on a consumer survey 

conducted by RTI International, Tennessee State University, and Kansas State University (Cates 

et al. 2006). The results of the survey indicated prepackaged deli meat was stored for statistically 

significant longer periods than deli meat sliced at retail. The survey did not find any difference 

for storage temperature. 

RESULTS

This risk assessment, using current retail contamination data for deli meat (Draughon, 2006) and 

current consumer behavior data for deli meats (Cates et al., 2006) indicates that of those 

listeriosis cases and deaths attributed to deli meats, approximately 83% are associated with deli 

meats sliced at retail. The estimated mean number of deaths per year from L. monocytogenes in 

retail-sliced deli meats was 166.9 (95% CI: 164.5 – 169.3). In contrast, the estimated mean 

number of deaths from prepackaged product was 34.1 (95% CI: 33.4 – 34.9). Similarly, 919.6 

(906.8-932.4) illnesses were attributed to retail-sliced product while 188.6 (184.7-192.4) 

illnesses were attributed to prepackaged product.

Of the four categories of RTE deli meat, most of the predicted deaths were attributed to retailsliced product (which had a higher starting concentration) without growth inhibitor (which 

allowed for greater growth rates). Almost 70% of all predicted deaths fell into this category. 

The results illustrate the significant interaction between slicing location and use of growth 

inhibitor.

Sensitivity analyses indicated that the percentage of deaths attributed to retail-sliced deli meats 

was not appreciably affected by consumer storage time, product shelf life, or total number of 

deaths.

CONCLUSIONS

Of those illnesses and deaths from L. monocytogenes from deli meat consumption, 

approximately 83% are attributed to deli meat sliced and packaged at retail facilities (Endrikat et 

al., 2010). The remainder is from prepackaged deli meat. Similar results were obtained by 

Pradhan et al. (2010) in a study that compared the risk of listeriosis in both retail-sliced and 

prepackaged ham and turkey. Studies are needed to determine how contamination of deli meat at 

retail occurs and to design effective interventions for reducing listeriosis associated with the 

consumption of deli meat sliced at retail.