In every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk. This sheet talks about whether listeriosis may increase the risk for birth defects above that background risk. This information should not take the place of medical care and advice from your health care provider.

What is listeriosis?

Listeriosis is an infection caused by Listeria monocytogenes bacteria, often called just Listeria. Listeriosis is typically caused by eating food that has been contaminated with Listeria. Some of the foods that are more likely to be contaminated with Listeria include unpasteurized (raw) milk, uncooked meat and fish, uncooked vegetables, lunch meat and soft cheeses.

Who is at risk for listeriosis?

People who may be more likely to get listeriosis include: pregnant women, young children, adults over the age of 60, and people with weakened immune systems. Following some simple food safety guidelines can reduce the chance of listeriosis.

What precautions should I take to avoid the infection?

To decrease the risk of listeriosis and other food-borne illness in all individuals:

  • Do not drink unpasteurized milk (also called raw milk) or eat any foods made with unpasteurized milk.
  • Thoroughly cook raw foods from animal sources.
  • Wash raw vegetables.
  • Separate uncooked meats from cooked meats and vegetables.
  • Wash your hands, cutting boards and knives after contact with uncooked foods.
  • Consume ready-to-eat foods as soon as possible.
  • Keep your refrigerator at or below 40 degrees Fahrenheit (4 degrees Celsius).
  • Clean your refrigerator regularly.

Pregnant women should take additional precautions to decrease the risk of listeriosis:

  • Do not eat soft cheeses (such as feta, Brie, Camembert, blue-veined cheeses and Mexican-style cheeses such as queso blanco, queso fresco and Panela) unless they have labels stating that they are made from pasteurized milk. It should be noted that some Mexican style cheeses made from pasteurized milk have been a source of Listeria infections possibly due to the cheese making process.
  • Reheat to steaming any leftover and ready-to-eat food, such as hot dogs, cold cuts and deli meat.
  • Take care to not get the juice of deli meats and hot dogs on other foods/surfaces and wash your hands after handling deli meats and hot dogs.
  • Do not eat refrigerated pâté, meat spreads or refrigerated smoked seafood, unless it is an ingredient in a fully cooked dish (like a casserole).

How do I know if I’ve been infected with Listeria?

Symptoms of listeriosis may range from showing no symptoms to having diarrhea, fever, muscle pain, joint pain, headache, stiff neck, backache, chills and sensitivity to bright light, or sore throat with fever and swollen glands. These symptoms can begin days to weeks after eating contaminated food. A blood test can confirm whether you have been infected with listeriosis. If you have eaten contaminated food and do not have symptoms, some experts feel no special testing or treatment is needed. Be sure to discuss this with your health care provider.

I am pregnant and have been infected with Listeria. Will this affect my baby?

Listeria infection during pregnancy can increase the risk of miscarriage, stillbirth, uterine infection and preterm delivery. Listeriosis has not been linked to a pattern of birth defects.

Listeriosis during pregnancy can also increase risk for health problems for the newborn. Newborn babies infected with Listeria will either have early or late onset listeriosis. Early onset listeriosis develops 1-2 days after birth, and the baby often has signs of a serious bacterial infection. Late onset listeriosis occurs one to two weeks after birth and usually includes symptoms of meningitis and is most likely related to Listeria present in the mother’s birth canal.

Not all babies whose mothers are infected during pregnancy will have problems due to listeriosis. Early diagnosis and treatment with high doses of antibiotics may prevent infection of the unborn baby and result in the birth of a healthy infant.

Are there any treatments for listeriosis during pregnancy?

Yes, large doses of antibiotics such as ampicillin or penicillin are generally recommended. Therapy for maternal listeriosis with high doses of antibiotics has resulted in successful therapy for the developing baby, leading to lower incidences of premature deliveries and stillbirths.

Is there any way to know if the baby has been infected or harmed by listeriosis?

An ultrasound to look at the baby can be used to check for an enlarged heart, thickened bowel, and increased thickness of the stomach walls, which may occur in some babies infected with Listeria. A blood test can be performed on the baby after birth to detect whether the baby has been infected with Listeria.

Can Listeria be passed to the baby through breast milk?

While it may be possible to pass Listeria on to an infant through breast milk, there are no reports of infection occurring in this way. Be sure to talk to your health care provider about all your choices for breastfeeding.

Does it matter if the baby’s father was exposed to Listeria before I got pregnant?

There is no evidence linking paternal exposure to Listeria with higher incidences of infection during pregnancy. In general, exposures that fathers have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures and Pregnancy at http://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/pdf/.

References Available By Request