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. The disease affects primarily pregnant women, newborns, and adults with weakened immune systems. It can be avoided by following a few simple recommendations.

What are the symptoms of listeriosis?

A person with listeriosis has:

  • Fever
  • Muscle aches
  • Sometimes gastrointestinal symptoms such as nausea or diarrhea.

If infection spreads to the nervous system, symptoms such as:

  • Headache
  • Stiff neck
  • Confusion
  • Possibly, loss of balance

Infected pregnant women may experience only a mild, flu-like illness. However, infections during pregnancy can lead to:

  • Premature delivery
  • Infection of the newborn
  • Stillbirth

How great is the risk for listeriosis?

In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year. Of these, 500 die. At increased risk are:

  • Pregnant women - about 20 times more likely than other healthy adults to get listeriosis (About one-third of listeriosis cases happen during pregnancy)
  • Newborns - suffer the serious effects of infection in pregnancy
  • Persons with weakened immune systems
  • Persons with cancer, diabetes, or kidney disease
  • Persons with AIDS - almost 300 times more likely to get listeriosis than people with normal immune systems
  • Persons who take glucocorticosteroid medications
  • The elderly

Healthy adults and children occasionally get infected with Listeria , but they rarely become seriously ill.

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 the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The bacterium 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 bacterium. 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.

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 Listeria infection by avoiding certain high-risk foods and by handling food properly.

Can listeriosis be prevented?

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

How can you reduce your risk for listeriosis?

General recommendations:

  • 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 raw (unpasteurized) milk or foods made from raw milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.

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

  • Avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and Mexican-style cheese. (Hard cheese, processed cheeses, cream cheese, cottage cheese, or yogurt need not be avoided.)
  • Leftover 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.

How do you know if you have listeriosis?

There is no routine screening test for susceptibility to listeriosis during pregnancy, as there is for rubella and some other congenital infections. If you have symptoms such as fever or stiff neck, consult your doctor. A blood or spinal fluid test (to cultivate the bacteria) will show if you have listeriosis. During pregnancy, a blood test is the most reliable way to find out if your symptoms are due to listeriosis.

What should you do if you've eaten a food recalled because of Listeria contamination?

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 two months become ill with fever or signs of serious illness, you should contact your physician and inform him or her about this exposure.

Can listeriosis be treated?

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, although a combination of antibiotics is often used until physicians are certain of the diagnosis. Even with prompt treatment, some infections result in death. This is particularly likely in the elderly and in persons with other serious medical problems.