FDA says time, temperature are keys to reducing Listeria risk

Oct 21, 2003 (CIDRAP News) – A painstaking analysis of the risk of Listeria infections associated with ready-to-eat (RTE) foods shows that proper refrigeration and limiting storage time could reduce the risk by more than 50%, the Food and Drug Administration (FDA) announced today.

RTE foods, such as hot dogs and deli meats, should be stored at 40º F or lower and should be used as soon as possible, the FDA said in releasing the 500-page risk assessment. However, the agency didn't say how long particular foods can be safely stored.

"The temperature at which these foods are held is the single most important thing," Joseph Levitt, director of the FDA's Center for Food Safety and Applied Nutrition (CFSAN), said in a news briefing. "The take-away message is that all the way through the food chain . . . these food products that are of highest concern should be kept at 40 degrees Fahrenheit. Second, consumers should consume these within a reasonable time and not keep them forever in their refrigerators."

Reformulation of products "so that they no longer support the growth" of Listeria monocytogenes could yield similar reduction in the risk of illness, the FDA said in a news release. The food industry is already using that approach to some extent, officials said.

On a per-serving basis, the foods posing the highest risk of listeriosis are deli meats, hot dogs (if not reheated), pate and meat spreads, unpasteurized milk, smoked seafood, and cooked RTE crustaceans, the FDA reported. The estimated risks for those foods range from 7.7 cases per 100 million servings for deli meats to 5.1 cases per billion servings for crustaceans.

The FDA repeated previous advice that people at high risk for listeriosis—pregnant women, older adults, and people with weak immune systems—should not eat high-risk foods. However, the risk assessment prompted one change in the advice: soft cheeses are now considered safe if they are made with pasteurized milk. The category includes Feta, Brie, Camembert cheeses, blue-veined cheeses, queso blanco, queso fresco, and Panela. Evidence that the risk is now linked specifically to cheeses made from unpasteurized milk reflects dairy industry and FDA efforts in recent years to control Listeria in soft cheeses, the agency said.

The FDA said people in high-risk groups should continue to avoid:

  • Hog dogs and luncheon meats unless they are reheated until steaming hot
  • Refrigerated pates or meat spreads (canned or shelf-stable forms may be eaten)
  • Refrigerated smoked seafood unless it is in a cooked dish, such as a casserole (canned or shelf-stable smoked seafood may be eaten)
  • Unpasteurized milk and foods that contain it

The report is a revision of a draft version that was released in January 2001. "We focused on Listeria because of its important public health impact," said Levitt. From surveillance in 1996 and 1997, the Centers for Disease Control and Prevention (CDC) estimated that Listeria-contaminated food caused 2,500 cases of illness and 500 deaths per year, according to the report. That represented the second-highest case-fatality rate of any foodborne pathogen.

Levitt said the latest data from the CDC indicate that listeriosis cases and deaths have dropped by about 40% since 1996-97, to about 1,500 cases with 300 deaths per year. "That's our current baseline. From that baseline, we believe that illnesses from Listeria can be reduced another 50% or more," he said.

In response to a question about how long RTE foods can be safely kept, Bob Buchanan, a CFSAN official at the news briefing, said, "As you might expect, the rate of growth [of Listeria] depends on the food, so it's difficult to give specific times at this point. We hope to provide further guidance and additional information."

Levitt commented, "The advice to consumers is, if it's getting old, don't eat it."

Levitt called the risk assessment "the most extensive of its type ever conducted," covering 23 food categories. Buchanan said the authors of the analysis reviewed more than 3,000 documents and "over half a million data points." Some data used in the report were provided by the Department of Agriculture's Food Safety and Inspection Service (FSIS).

The FDA said it will develop "an action plan to identify additional measures to reduce the risks of listeriosis." The plan will include guidance for food processors, retailers, and food service establishments; training and technical assistance; information for consumers and healthcare providers; enforcement and regulatory strategies; disease surveillance and outbreak response; and research needs.

The FDA, FSIS, and CDC will hold a public meeting Dec 4 to present the risk assessment and give the public a chance to ask questions and offer comments.

See also:

Summary of the risk assessment (27 pages)

Risk assessment table of contents with links to full-text sections

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