New tool for retail delis targets Listeria contamination

May 13, 2013 (CIDRAP News) – Federal food regulators unveiled an extensive study of how Listeria monocytogenes behaves in a retail delicatessen that they hope merchants, food producers, and even consumers will use as a "virtual deli" to better understand contamination and prevention steps.

The draft risk assessment report was produced by the US Department of Agriculture (USDA) and the Food and Drug Administration (FDA), with input from academic institutions, the Centers for Disease Control and Prevention (CDC), and other stakeholders. Federal agencies released the 179-page document on May 10.

Listeria monocytogenes is problematic in deli settings, because it can contaminate food processing plants and processed meats and grow in cold temperatures. Meat slicing and other practices in delicatessen settings can also pose a risk of product cross-contamination. Also, food sold in delis is often eaten without being heated, a step that could kill the pathogen.

Elizabeth Hagen, MD, USDA's undersecretary for food safety, said the report's findings are designed to drive down the 1,600 Listeria infections, 260 of them fatal, that typically occur each year. "This assessment highlights the importance of our work to prevent [L monocytogenes] from entering the retail environment in the first place, and provides a significant tool toward this effort to protect consumers and prevent foodborne illness."

President Obama's Food Safety Working Group flagged the Listeria assessment as a priority, and work began on the project in the fall of 2008, according to the report's summary. Federal officials are hosting a public meeting on May 22 in Washington, D.C., to discuss the report's findings and are seeking public comments on it by Jul 12, according to a Federal Register notice today.

The study quantitatively links retail deli practices to predicted public health outcomes, which has never been done before, the USDA said. Researchers who worked on the study included the work routines of deli workers, contamination concentrations of incoming foods, environmental contamination sites, and dose-response probabilities in their model inputs.

Group members even set up a mock deli to study the dynamics of Listeria transfer during actions such as preparing, slicing, and packaging deli foods. They also incorporated data on Listeria prevalence, level, and subtype detected from 30 retail delis in three grocery chains in three different states.

The probe found that no single intervention will curb Listeria in food sold at retail delis. Instead, there are a host of steps that deli operators and suppliers can take to reduce the risk, which focus on four main areas: storage temperature, growth inhibition, cross contamination, and contamination of incoming products.

For example, keeping refrigerated ready-to-eat foods at 41°F or colder, as recommended in the FDA Food Code, could prevent at least 9 of every 100 listeriosis cases, according to the report.

Reformulating deli products that support the growth of Listeria to include growth inhibitors could have the largest impact, preventing 96 of 100 illness cases, the report said. However, the true impact of the intervention would likely be smaller, because growth inhibitors may be used in concentrations that don't cover the shelf life of the food, and they can affect the flavor of the food.

Slicers in deli settings present a difficult cross-contamination challenge, the report says, but proper cleaning and personal hygiene can make a difference.

If food processors cut the levels of Listeria in ready-to-eat foods by half, 22 of 100 cases of listeriosis from tainted deli products could be avoided, according to the report. The USDA said that findings suggest that continued efforts to curb low-level contamination during processing, even in products that don't support Listeria growth, reduce the risk of those and other products from being cross-contaminated in delis.

See also:

May 10 USDA press release

Full risk assessment

May 13 Federal Register notice

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