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Ohio State University Extension Fact Sheet

Family and Consumer Sciences

1787 Neil Avenue, Columbus, Ohio 43210-1295


One Tough Bug


Nancy Stehulak

Listeria are bacteria found frequently in the environment. One listeria species, Listeria monocytogenes, can cause the serious foodborne illness "listeriosis." Listeriosis is a bacterial infection. Approximately 425 deaths occur each year in the United States due to L. monocytogenes.

L. monocytogenes is somewhat unusual in that it will grow at refrigeration temperatures. It is slightly more heat resistant than many other bacteria such as salmonella and E. coli, and will grow at temperatures as high as 140 to 150 degrees F. It will not survive pasteurization or heat treatment. Freezing seems to have little effect on the bacteria.

Where does L. monocytogenes come from?

L. monocytogenes has been found in soil, leaf litter, sewage, silage, dust, and water. The organism often moves through animals and humans without causing illness, and has been found in many domestic and wild animals, including birds and fish. It has only been in the last decade that L. monocytogenes has been recognized as an agent of foodborne illness.

Who is at risk?

Healthy people rarely contract listeriosis, but the illness can be serious for some people, especially the elderly, newborns, pregnant women, and those with weakened immune systems.

Foods Associated with Listeriosis

L. monocytogenes has been associated with such foods as raw milk, unpasteurized milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, raw-meat sausages, raw and cooked poultry, raw meats (all types), and raw and smoked fish. Its ability to grow at temperatures as low as 37 degrees F permits multiplication in refrigerated foods.

The Illness-What are the symptoms?

Consumers most commonly contract listeriosis by eating food contaminated with the organism. Healthy people do not often develop noticeable listeriosis symptoms after eating food containing L. monocytogenes. The highest incidence of listeriosis has been in persons over 60 years old and newborns. Infections that occur during pregnancy may lead to miscarriages or serious illness in newborns. Others most at risk include those with compromised immune systems due to cancer, AIDS, or medications that impact the immune system.

Symptoms are fever, fatigue, nausea, vomiting, and diarrhea. More serious symptoms can result in meningitis (brain infections) and septicemia (bacteria in the bloodstream). Pregnant women may contract flu-like symptoms of listeriosis; complications can result in miscarriage, stillbirth, or meningitis in the newborn.

How can I reduce my risk?

L. monocytogenes in food cannot be seen, tasted, or smelled. Common sense and simple precautions that apply to any foodborne illness should be used. Good sanitation, personal hygiene, and safe buying, storing, cooking, and serving methods, when applied in home, retail, and food service environments, can reduce the risk of problems with L. monocytogenes.

Although most of the population is at very low risk for listeriosis, the risk can be reduced if you:

  1. Thoroughly cook all food of animal origin.
  2. Wash raw vegetables thoroughly before eating.
  3. Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods.
  4. Avoid raw/unpasteurized milk or foods made from raw milk.
  5. Wash hands, knives, and cutting boards after handling uncooked foods.
  6. Read and follow label instructions to "keep refrigerated" and "use by" a certain date.



  1. U.S. Department of Agriculture, Food Safety and Inspection Service, Background Document March 1992. Preventing Foodborne Listeriosis.

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