Listeria and miscarriage, is there a risk?

In 2008, the United States Department of Agricultural stepped up a media education campaign regarding food safety in general and infection with Listeria in particular. They stressed that pregnant women are at high risk for getting sick from Listeria and that listeriosis (Listeria infection) can cause miscarriage and other complications of pregnancy.

What is Listeria?

Listeria is a type of bacteria found everywhere – in soil and ground water and on plants. Women can carry Listeria in their bodies without becoming sick. Most infections in women result from eating contaminated foods. Most people are not at increased risk for listeriosis. Hormonal changes during pregnancy have an effect on the mother’s immune system that lead to an increased susceptibility to listeriosis in a pregnant woman. In fact, Listeria infection is about 20 times more common in pregnant women than in the general population. Pregnant women account for 27% of all listerial infections.

Listeria symptoms in pregnant women

Because the symptoms of listeriosis can take a few days or even weeks to appear and can be mild, you may not even know you have it. In pregnant women, listeriosis may cause flu-like symptoms with the sudden onset of fever, chills, muscle aches, and sometimes diarrhea or upset stomach. The severity of the symptoms may vary. If the infection spreads to the nervous system, the symptoms may include headache, stiff neck, confusion, loss of balance, or convulsions. A blood culture can be performed to find out if your symptoms are caused by listeriosis.
Listeria can cross the placenta and affect a fetus.

Listeriosis and miscarriage

I reviewed the medical literature and found there is actually very little data linking listeriosis to miscarriage in human beings. Most of the research on the effects of Listeria in pregnancy that is available mostly involves problems later in the 2nd or third trimester or the study reported on a few isolated cases. In 1991, the only large scale study of women with recurrent early miscarriage was conducted.
Uterine tissue and swabs from the cervix were obtained and tested for the presence of Listeria. During the 10-year study period, none of the patients with recurrent miscarriage were found to have the bacteria. The study authors concluded that Listeria may contribute to miscarriage, but probably not on a recurrent basis. Routine testing for Listeria in an asymptomatic woman in a clinical setting is not cost-effective and is therefore unwarranted. They also concluded that it is unwarranted to give routine administration of antibiotics to treat Listeria to women who have had a history of recurrent miscarriage.
That being said, it is not unreasonable for a pregnant woman to follow the safety measures for reducing the chance of becoming sick with a food borne illness.
  • Do not eat hot dogs, luncheon meats like bologna, or deli meats unless they are reheated until steaming hot.
  • Do not eat soft cheeses such as feta, Brie, Camembert, blue-veined cheeses, and Mexican-style cheeses such as “queso blanco fresco” unless it is labeled as made with pasteurized milk. Make sure the label says “Made with Pasteurized Milk”.
  • Hard cheeses, semi-soft cheeses such as mozzarella, pasteurized processed cheese slices and spreads, cream cheese, and cottage cheese can be safely consumed.
  • Do not eat refrigerated pâté or meat spreads. Canned or shelf-stable pâté and meat spreads can be eaten.
  • Do not eat smoked seafood found in the refrigerated section of the store unless it is an ingredient in a cooked dish such as a casserole.

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Examples of refrigerated smoked seafood include salmon, trout, whitefish, cod, tuna, and mackerel which are most often labeled as ‘nova-style,” “lox”, “kippered”, “smoked”, or “jerky”. This fish is found in the refrigerated section or sold at deli counters of grocery stores and delicatessens. Canned fish such as salmon and tuna or shelf-stable smoked seafood may be safely eaten. 
  • Do not drink raw (unpasteurized) milk or eat foods that contain unpasteurized milk.
  • Use all perishable items that are precooked or ready-to-eat as soon as possible.
  • Clean your refrigerator regularly using hot water and soap.
  • Clean up all spills in your refrigerator right away – especially juices from hot dog packages or raw meat or chicken or turkey.
  • Use a refrigerator thermometer to make sure that the refrigerator always stays at 40º F or below and a freezer temperature of 0º F or below.
  • Wash your hands after you touch hot dogs, raw meat, chicken, turkey or seafood or their juices.
According to the CDC website, “if you have eaten a contaminated product and do not have any symptoms, most experts believe you don’t need any tests or treatment, even if you are pregnant. However, you should inform your physician or healthcare provider if you are pregnant and have eaten the contaminated product, and within 2 months experience flu-like symptoms.”