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Listeriosis Exposure Can Result in Stillbirth


Women are often counseled on the appropriate diet during pregnancy, including foods to avoid because of the risk to the unborn child. Researchers now say Listeria monocytogenes, a food-borne pathogen that is one of the most dangerous in the United States, poses an even greater risk to pregnant women and their fetuses than previously thought.

Listeria has the ability to cross the placenta and may infect the baby leading to a threat to the baby’s life, including miscarriage or stillbirths.

Mary Alice Smith, PhD, and colleagues at the University of Georgia in Athens studied data from both animal studies and epidemiological research and reported their findings in the November issue of Risk Analysis. The amount currently recognized by the USDA, the FDA, and the CDC for “median lethal dose” is much larger than the amount now suspected to cause harm.

Median lethal dose is the concentration of a toxic substance required to kill half of a tested population.

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Dr. Smith found that the risk of fetal or infant mortality among pregnant women who consume a food containing one million cells of L. monocytogenes is estimated at about 50%. The previous risk assessment estimated that it would take more than 10 trillion cells to result in the same rate.

Foods most often contaminated with the pathogen include deli meats, pasteurized dairy products, smoked seafood, and raw foods. L. monocytogenes has also been isolated from pasteurized and refrigerated foods such as fluid milk and soft-ripened cheeses, such as Mexican-style queso, the authors noted.

Because about 48,000 servings of soft cheeses are consumed in the United States by pregnant women, according to consumption estimates in the USDA’s Continuing Survey of Food Intake by Individuals and NHANES III, researchers predict that there could be as many as eight stillbirths a year from eating tainted cheese. The researchers caution, however, that this number is an estimate and could vary depending upon contamination levels.

In the United States, the CDC estimates that 2,500 cases of listeriosis occur annually, leading to 500 deaths. About a third of those occur in pregnant women. Death is more likely for those with compromised immune systems, fetuses and newborns, and in the elderly. In addition, listeriosis can cause premature delivery, lead to neurological dysfunction, mental retardation, or hearing loss in the newborn.

Women can become infected at any point in the pregnancy, but most cases are reported in the third trimester. The mother may not have symptoms, or experience only mild symptoms, but pass the infection onto the fetus. Women are encouraged during pregnancy to avoid deli meats, unless heated, soft cheeses such as Brie, Feta or Mexican queso, or unpasteurized products such as raw milk.

Additional Sources Include: The American Pregnancy Association