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. Listeria can be found in your home, in restaurants and other places such as the grocery store or food processing plants. Food with Listeria can introduce the infection into the refrigerator which can spread to other foods. Listeria can continue to live in cold temperatures, such as in the refrigerator, but the chance for spreading can be slowed if the refrigerator is kept at a temperature of 40 degrees Fahrenheit or lower.

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. However, the largest recent outbreak occurred in cantaloupes.

Who is at risk for listeriosis?

The people most vulnerable to 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.
  • Heat foods to at least 165°F (to steaming), to kill the bacterium.
  • Wash raw vegetables and fruit, even if you plan to peel them (to remove skin).
  • Separate uncooked meats from cooked meats and vegetables.
  • Wash your hands, cutting boards, knives, counters, and sinks 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. However, 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 at least 165°F / to steaming, any leftovers, ready-to-eat foods, hot dogs, cold cuts, deli meat, frozen vegetables and frozen prepared foods.
  • 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 hummus, pâté, meat spreads or refrigerated smoked seafood, unless it is an ingredient in a fully cooked dish (like a casserole).
  • Avoid ready to eat salads.

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

Not everyone affected with Listeria will develop symptoms. Symptoms of listeriosis range from showing no symptoms to having diarrhea, fever, muscle pain, joint pain, headache, stiff neck, backache, chills, sensitivity to bright light, and/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 pregnancy or the baby?

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

Listeriosis during pregnancy can also increase the chance for serious health problems for the newborn. Newborn babies infected with Listeria can develop either early onset 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 1-2 weeks after birth, and usually includes symptoms of meningitis. Late onset listeriosis 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 might prevent infection of the unborn.

Are there any treatments for listeriosis during pregnancy?

Yes, large doses of antibiotics have been recommended. Therapy for maternal listeriosis with high doses of antibiotics has resulted in successful therapy, leading to lower incidences of premature deliveries and stillbirths. Your healthcare providers will talk with you about the right treatment for your pregnancy.

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?

It is unknown if Listeria can be transmitted through breast milk. If you have been diagnosed with Listeria and are breastfeeding, talk to your healthcare provider.

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 a higher chance 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 on Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/pdf/.

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