Listeria (Listeriosis)

Fact sheet about Listeriosis

What is listeriosis?

Listeriosis is an infection caused by bacteria called Listeria monocytogenes. The infection is most dangerous for pregnant women, newborns, older adults, and adults with weakened immune systems.

Who gets listeriosis?

Anyone can get listeriosis. However, the following people have a higher risk of serious illness:

  • Pregnant women 
  • Unborn babies and newborns
  • People with cancer, diabetes, kidney or liver disease
  • People with HIV infection
  • People who take steroid medications or are on chemotherapy
  • Older adults

Healthy adults and children occasionally get infected with Listeria, but they are usually not seriously ill.

How is listeriosis spread?

People usually get listeriosis by eating food containing Listeria bacteria. Veterinarians, farmers, and others who work with animals may become infected through direct contact with infected animals. Babies can be born with listeriosis if their mothers eat food containing Listeria during their pregnancy.

How does Listeria get into food?

Listeria monocytogenes is found in soil and water. Vegetables and fruits, such as whole melons, can become contaminated from the soil or from manure used as fertilizer. Animals can carry Listeria without appearing ill, and can contaminate other foods such as meats and dairy products. Listeria has been found in many raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated during or after processing, such as soft cheeses, cold cuts, smoked fish products, and ready-to-eat products such as crabmeat and chicken. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain Listeria.

What are the symptoms of listeriosis?

A person with listeriosis usually has fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. Many people develop only mild symptoms. 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 have mild, flu-like symptoms; but infection during pregnancy can lead to premature delivery, infection of the newborn, or even stillbirth.

How is listeriosis treated?

Listeriosis can be treated with antibiotics. When infection occurs during pregnancy, antibiotics can often prevent infection of the fetus or newborn. Babies with listeriosis can be given the same antibiotics as adults.

How can listeriosis be prevented?

The following measures can be taken to reduce a person’s chance of getting sick with listeriosis:

  • Thoroughly cook all raw meats.
  • Wash raw vegetables before eating.
  • Scrub the surface of melons, such as canteloupes, watermelon, or honeydew, before cutting and wash hands with warm water and soap for 20 seconds before and after handling.
  • Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods.
  • Wash hands, knives, and cutting boards with soap and water after handling uncooked meats.
  • Avoid raw (unpasteurized) milk or foods made from raw milk.
  • Always thaw ready-to-eat frozen food in the refrigerator or microwave, not on a counter.
  • Before eating, thoroughly reheat leftover food until steaming hot.

People at higher risk for listeriosis, such as pregnant women and persons with weakened immune systems, should also do the following:

  • Avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and Mexican-style cheese unless the label says “MADE WITH PASTEURIZED MILK”. (Hard cheeses, processed cheeses, cream cheese, cottage cheese, or yogurt need not be avoided.)
  • Avoid hot dogs, deli meats, or fermented or dry sausages unless they are heated until steaming hot just before serving.
  • Wash hands after handling hot dog and deli meats, and clean all utensils and food preparation surfaces in contact with these food items.

Where can I get more information?

  • Your doctor, nurse or clinic
  • Your local board of health (listed in the telephone directory under “government”)
  • The Centers For Disease Control and Prevention website
  • The Massachusetts Department of Public Health, Division of Epidemiology and Immunization at (617) 983-6800 or toll-free at (888) 658-2850.

Spanish and Portuguese translations of this fact sheet are available under additional resources.

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