What is listeriosis?

Listeriosis, which is caused by eating food contaminated by the bacteria Listeria monocytogenes, can be a serious disease. In the United States, an estimated 1,850 persons become seriously ill with listeriosis each year. Of these, 425 die. In Illinois, approximately 20 cases of listeriosis are reported annually; about 25 percent of the cases die.

Who is at risk for listeriosis?

While anyone can become ill from eating food contaminated by the bacteria, pregnant women, newborns and adults with weakened immune systems are most at risk. Pregnant women are about 20 times more likely than other healthy adults to get listeriosis. About one-third of all reported cases happen during pregnancy. Infection during pregnancy may result in spontaneous abortion during the second and third trimesters or stillbirth.

Those with weakened immune systems (for example, the elderly and persons with cancer, diabetes or kidney disease or HIV/AIDS) are more likely to get listeriosis than people with normal immune systems.

How does a person get listeriosis?

You get listeriosis from eating food contaminated by the bacteria. Babies can be born with the disease if their mothers ate contaminated food during pregnancy. Although healthy adults and children may consume contaminated food without becoming ill, those who are at increased risk can probably get the disease after consuming even a few bacteria.

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 bacteria without appearing ill and meat or dairy products from these animals can be contaminated. The bacteria also have been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed food, that become contaminated after processing, such as cheese and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from raw milk may contain the bacteria.

How do you know if you have listeriosis?

A person with listeriosis usually has a fever, muscle aches and, sometimes, gastrointestinal symptoms such as nausea and 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, infection during pregnancy can lead to premature delivery, infection of the newborn or even stillbirth.

There is no routine screening test for susceptibility to listeriosis during pregnancy, as there is for rubella or some other congenital infections. If you have symptoms such as fever or stiff neck, you should consult your physician. 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 symptoms are due to listeriosis.

How can you reduce your risk for listeriosis?

As with other foodborne illnesses, there are several guidelines that will help to reduce the risk of infection with Listeria monocytogenes:

• Cook thoroughly any 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 and ready-to-eat foods.
• Avoid raw (unpasteurized) milk or foods made from raw milk.
• Wash hands, knives and other utensils, and cutting surfaces after handling uncooked foods.

Persons who are at high risk — pregnant women and persons with weakened immune systems — should follow these additional recommendations:

• Avoid soft cheeses (for example, feta, Brie, Camembert, blue-veined and Mexican- style cheese). Hard cheeses, processed cheeses, cream cheese, cottage cheese or yogurt need not be avoided.
• Cook left-over foods or ready-to-eat foods, such as hot dogs, until steaming hot before eating.
• Although the risk of listeriosis associated with foods from deli counters is relatively low, pregnant women and persons whose immune systems are suppressed may choose to avoid these foods or to thoroughly reheat cold cuts before eating.

How is listeriosis treated?

When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or the newborn. Babies with listeriosis receive the same antibiotics as adults.

Even with prompt treatment, however, some infections result in death. This is particularly likely in the elderly and in persons with other serious medical problems.