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Listeria Monocytogenes Contamination in Foods


Preventing Listeria Contamination in Foods

By Carol Rados
FDA Consumer magazine, Jan-Feb 2004

Listeria monocytogenes (L. monocytogenes) is a harmful bacterium that can be found in a variety of foods. In pregnant women, L. monocytogenes-caused illness can result in miscarriage, fetal death, or severe illness or death of a newborn infant. The elderly and those with weakened immune systems are also at risk for severe illness or death from L. monocytogenes-contaminated food.
Source: FDA/CDC 2003 Update of the Listeria Action Plan

Keeping ready-to-eat foods cold is key to reducing listeriosis, a serious infection in humans. That's one of the conclusions of a recent Food and Drug Administration risk assessment on the relationship between foodborne listeriosis and human health.

Listeriosis is an illness caused by eating foods contaminated with Listeria monocytogenes, bacteria found in soil and water. Food-producing animals can carry these bacteria in their intestines. As a result, the disease-causing bacteria may be spread to meat and dairy products. Ready-to-eat foods also can become contaminated within the processing plant, after processing, or along the route from plant to plate.

Listeriosis has been recognized as an important public health problem in the United States. Scientific information from the FDA's risk assessment outlines measures that industry, retailers and consumers can take to dramatically reduce the risk of this potentially fatal infection.

Listeriosis causes flu-like symptoms, such as fever and chills. Sometimes people have an upset stomach. If the infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur.

Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. Although healthy people may consume contaminated foods without becoming ill, those at increased risk for infection--people over 60, newborns, and people with weakened immune systems--are more likely to get listeriosis after eating food contaminated with even a few bacteria. People at risk can prevent the infection by avoiding certain high-risk foods and by handling food properly.

Outbreaks of listeriosis are associated with ready-to-eat foods such as hot dogs, luncheon meats, cold cuts, soft cheeses, deli-style meats, and poultry. Although listeria bacteria are killed with thorough cooking or by other heating methods, such as pasteurization, these tough bugs can grow in the refrigerator and survive in the freezer. The FDA and the Centers for Disease Control and Prevention (CDC) advise that the most important things consumers can do to reduce the risk of illness are:

  • Store ready-to-eat foods at 40 degrees Fahrenheit or lower--use a refrigerator thermometer to check the temperature.
  • Use perishable and ready-to-eat foods as soon as possible.
  • Clean the refrigerator regularly.

Although listeriosis is potentially life-threatening, the CDC's FoodNet program has recorded over a 40 percent decrease in its incidence during the past five years. The results of the risk assessment reinforce past studies that found that, even though foodborne listeriosis is rare and declining, it remains a public health concern. The CDC estimates that in the United States, 2,500 people become seriously ill with listeriosis each year, and of these, 500 die.


The following advice is provided for pregnant women, older adults, and people with weakened immune systems who are at higher risk for listeriosis:

  • Do not eat hot dogs and luncheon meats, unless they are reheated until steaming hot.
  • Do not eat soft cheese such as feta, brie, and Camembert, blue-veined cheeses, queso blanco, queso fresco, and Panela, unless it is labeled as made with pasteurized milk.
  • Do not eat refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." These fish are found in the refrigerated section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.
  • Do not drink unpasteurized milk or eat foods that contain unpasteurized milk.

How to Prevent Listeriosis and Other Foodborne Illnesses
Follow these four basic steps to food safety promoted by the food safety education program called Fight BAC!

  • Clean: Wash hands and surfaces often with hot, soapy water. Always wash hands, cutting boards, dishes, and utensils with hot, soapy water after they come in contact with raw food.
  • Separate: Don't cross-contaminate. Keep uncooked foods separate from vegetables, fruits, breads, and other foods that are already prepared for eating.
  • Cook: Cook to safe temperatures. If you are at risk for listeriosis, reheat luncheon meats, cold cuts, and other deli-style meat and poultry until they are steaming hot.
  • Chill: Refrigerate or freeze perishables, including ready-to-eat foods, promptly.

For More Information
Preventing foodborne illness

Listeriosis risk assessment



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