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Bureau of Disease Control

Listeriosis

What Is listeriosis?

Listeriosis is a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes. It has recently been recognized as an important public health problem in the United States. The disease affects primarily pregnant women, newborns, and adults with weakened immune systems. Healthy adults and children occasionally get infected with Listeria, but they rarely become seriously ill.

In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year, and about 500 people die. The risk of an individual person developing Listeria infection after consumption of a contaminated product is very small. If you have eaten a contaminated product and do not have any symptoms, we do not recommend that you have any tests or treatment, even if you are in a high-risk group. However, if you are in a high-risk group, have eaten the contaminated product, and within 2 months become ill with fever or signs of serious illness, you should contact your physician and inform him or her about this exposure.

What are the symptoms?

A person with listeriosis has fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. If infection 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 premature delivery, infection of the newborn, or even stillbirth. Healthy adults and children occasionally get infected with Listeria, but they rarely become seriously ill.

How is listeriosis treated?

Most people infected with the bacteria do not require any treatment other than supportive (rest and lots of fluids). When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or newborn. Babies with listeriosis receive the same antibiotics as adults.

How do people catch this disease?

You get listeriosis by eating food contaminated with Listeria. The bacteria is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The bacteria 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 the bacteria. Listeria is killed by pasteurization, and heating procedures used to prepare ready-to-eat processed meats should be sufficient to kill the bacterium; however, unless good manufacturing practices are followed, contamination can occur after processing.

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.

What can be done to stop the spread of this disease?

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, cooked foods and ready-to-eat foods. Avoid raw (unpasteurized) milk or foods made from raw milk. Wash hands, knives, and cutting boards after handling uncooked foods.

People at high risk, such as pregnant women and persons with weakened immune systems, should avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and Mexican-style cheese. (Hard cheeses, processed cheeses, cream cheese, cottage cheese, or yogurt need not be avoided.) Left-over foods or ready-to-eat foods, such as hot dogs, should be cooked until steaming hot before eating. Although the risk of listeriosis associated with foods from deli counters is relatively low, pregnant women and immunosupressed persons may choose to avoid these foods or thoroughly reheat cold cuts before eating.

Early detection and reporting of outbreaks of listeriosis to local and state health departments can help identify sources of infection and prevent more cases of the disease.