Listeriosis is a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes. Listeriosis primarily affects pregnant women, newborns, and adults with weakened immune systems.

In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year. Of these, 500 die. Pregnant women are about 20 times more likely than other healthy adults to get listeriosis. About one-third of listeriosis cases happen during pregnancy. Other people at risk include newborns (who suffer the serious effects of infection in pregnancy rather than the pregnant women themselves), people with cancer, diabetes, or kidney disease, people with AIDS (almost 300 times more likely to get listeriosis than people with normal immune systems), people who take glucocorticosteroid medications, and the elderly.

Listeriosis Symptoms

Symptoms of listeriosis include fever, muscle aches, and sometimes gastrointestinal symptoms (nausea or diarrhea). If listeriosis spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur.

Infected pregnant women may experience only a mild flu-like illness; however infections during pregnancy can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn. Newborns rather than the pregnant women themselves suffer the serious effects of infection in pregnancy.

How does Listeria get into food?

Listeria monocytogenes is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer.

Animals can carry Listeria without appearing ill and can contaminate foods of animal origin such as meats and dairy products. Listeria has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain Listeria.

Listeria is killed by pasteurization and cooking. However, in certain ready-to-eat foods such as hot dogs and deli meats, contamination may occur after cooking but before packaging.

How do you get listeriosis?

You get listeriosis by eating food contaminated with Listeria. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. Although healthy persons may consume contaminated foods without becoming ill, those at increased risk for infection can probably get listeriosis after eating food contaminated with even a few bacteria. Persons at risk can prevent listeriosis by avoiding certain high-risk foods and by handling food properly.

The general guidelines recommended for the prevention of listeriosis are similar to those used to help prevent other foodborne illnesses, such as salmonellosis.