Listeria infection

What is listeriosis?

Listeriosis, a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes, has recently been recognized as an important public health problem in the United States. Symptoms can show up 1-70 days after exposure to contaminated food and may include vomiting, nausea, cramps, diarrhea, headache, constipation or fever. Some infections become severe and develop into an infection of the brain or lining of the brain and blood poisoning. Some people experience only mild flu-like symptoms.

Who gets listeriosis?

While healthy adults and children occasionally get infected with Listeria, they rarely become seriously ill. The disease affects primarily older adults, pregnant women, newborns and adults with weakened immune systems. Each year in the U.S. about 1,600 persons become seriously ill with listeriosis, and of these 260 die. Pregnant women are about 20 times more likely than other healthy adults to get listeriosis and are at greatest risk in the third trimester. However, it is the newborn, rather than pregnant women, that suffer the serious effects of infection during pregnancy. Listeria infection during pregnancy can result in miscarriage, premature delivery or death to the newborn. Early treatment may prevent fetal infection and fetal death. Additionally, persons with AIDS are almost 300 times more likely to get ill from this infection than people with normal immune systems.

How do you get listeriosis?

When someone eats food contaminated with Listeria, they may become infected and then ill. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. While healthy people may consume contaminated foods without becoming ill, those at increased risk may become ill after eating food contaminated with even a few bacteria.

How is listeriosis treated?

When infection occurs during pregnancy, antibiotics given promptly can often prevent infection of the fetus or newborn. A person in a high-risk category who experiences flu-like symptoms within two months of eating contaminated food should seek medical care and tell the physician or healthcare provider about eating the contaminated food.

  • If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for persons at high risk for listeriosis.
  • Even with prompt treatment, some infections result in death, particularly in the elderly and in persons with other serious medical problems. Antibiotics used in the treatment of listeriosis include ampicillin, vancomycin, ciprofloxacin, linezolid and azithromycin.

How does Listeria get into food?

Listeria is a bacteria found in soil and water. Vegetables may become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacteria without being ill and contaminate foods like meats and dairy products. Listeria has been found in a variety of raw foods, such as uncooked meats and vegetables, unpasteurized milk and milk products. Additionally, processed foods such as soft cheeses and cold cuts at the deli counter may become contaminated after processing. Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods such as hot dogs and deli meats, contamination may happen after cooking and before packaging. In the 2008 Canadian outbreak, the contamination occurred in a food processing plant and there were possibly 220 contaminated products, including deli meats. Since the bacteria traveled through deli meats that were cooked (and therefore usually free of pathogens), the contamination probably occurred during packaging. The recall, closure and cleaning of the plant, training of personnel and expert management cost the company at least $20 million.

Can listeriosis be prevented?

The risk of listeriosis can be reduced by following general guidelines for food safety. These include:

  • Thoroughly cook raw food from animal sources, such as beef, pork or poultry.
  • Wash raw vegetables thoroughly before eating.
  • Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods.
  • Avoid unpasteurized (raw) milk or foods made from unpasteurized milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.
  • Consume perishable and ready-to-eat foods as soon as possible.

Recommended for persons at higher risk, such as pregnant women and persons with weakened immune systems, in addition to the recommendations listed above:

  • Do not eat hot dogs, luncheon meats, or deli meats unless they are reheated until steaming hot.
  • Avoid getting fluid from hot dog packages on other foods, utensils and food preparation. surfaces, and wash hands after handling hot dogs, luncheon meats and deli meats.
  • Do not eat soft cheeses such as feta, Brie, Camembert, blue-veined cheeses or Mexican style cheeses such as queso blanco unless clearly labeled that they are made from pasteurized milk.
  • Do not eat refrigerated pates or meat spreads.
  • Do not eat refrigerated smoked seafood unless it is contained in a cooked dish, such as a casserole.

While listeriosis is a potentially serious infection, it is rare, preventable and treatable. Taking care with food preparation is the single greatest safety measure we can take to protect our families and ourselves.

Additional resources
Listeria—Centers for Disease Control and Prevention
Food—U.S. Food and Drug Administration
Listeriosis—Infection Prevention and You