Listeriosis

What is listeriosis?

Listeriosis is usually caused by eating food contaminated with the Listeria monocytogenes bacteria. The illness develops when the bacteria get into the blood or other site inside the body.

Who gets listeriosis?

Listeriosis primarily affects older adults, pregnant women, newborns, and adults with weakened immune systems. Persons without these risk factors can sometimes be affected.

Where are Listeria found?

The Listeria bacteria are commonly found in soil and water.

How are Listeria bacteria spread?

Consuming raw or contaminated milk, soft cheeses, unwashed raw vegetables and fruits, undercooked poultry, and ready-to-eat meats such as deli meats can cause infection. Infection can also be transmitted from a pregnant woman to her baby in the womb or during birth. Veterinarians, farmers, and others who work with animals can become infected through direct contact with infected animals.

What are the symptoms of listeriosis?

Listeriosis usually causes fever and muscle aches, sometimes occurring after diarrhea or other gastrointestinal symptoms. Other symptoms may include headache, stiff neck, confusion, loss of balance, and convulsions. Pregnant women with listeriosis typically experience only a mild, flu-like illness, but infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn. In older adults and persons with weakened immune systems, a serious blood infection or meningitis is most commonly seen. People with healthy immune systems may experience a mild illness with fever or no symptoms at all.

How soon after exposure do symptoms appear?

Symptoms of invasive listeriosis generally appear about 2 or 3 weeks after exposure, but may appear up to 70 days after exposure.

How is listeriosis diagnosed?

Laboratory tests are needed to confirm the presence of the Listeria bacteria in samples of blood or cerebrospinal fluid of persons with symptoms of listeriosis.

What is the treatment for listeriosis?

Listeriosis can be treated with antibiotics. Persons who are pregnant, elderly, or have weakened immune systems and who experience flu-like symptoms within 2 months of eating contaminated food should seek medical care and tell the health care provider about eating the contaminated food. If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for persons at high risk for listeriosis. 

How can listeriosis be prevented?

A person can lower the risk of becoming infected by following these recommendations:

  • Pregnant women and persons with weakened immune systems should avoid soft cheeses, heat all leftovers and ready-to-eat foods, and either avoid hot dogs, luncheon meats, and other cold cuts or heat them before eating.
  • Thoroughly cook meats and poultry.
  • Thoroughly wash raw produce, such as fruits and vegetables, before eating them.
  • Avoid raw milk and other unpasteurized dairy products.
  • Keep uncooked meats separate from vegetables and cooked foods.
  • Wash knives, cutting boards, and kitchen surfaces after contact with uncooked foods.
  • Practice proper handwashing to prevent the bacteria from entering the mouth.
  • Clean the refrigerator regularly especially after spills from ready-to-eat food packages, raw meat, and raw poultry. 

How long can an infected person carry and shed the Listeria bacteria?

Infected persons can carry and shed the bacteria in their stool for several months. Mothers of infected newborn infants can shed the bacteria in vaginal discharges and urine for 7 to 10 days after delivery.

Should a person infected with Listeria be excluded from work or school? 

Most persons with listeriosis will be too ill to work. People who have diarrhea should not work as food handlers, or provide care for children or patients. Children who have diarrhea should not go to child care. Most infected people may return to work or school 24 hours after diarrhea stops, provided that they are careful to wash their hands with warm water and soap after using the toilet. 

How can I get more information about listeriosis?

February 2018