Why are pregnant women at higher risk from foodborne illness than other people?
Pregnant women are more susceptible only to certain kinds of food-borne illness, particularly listeriosis. While serious infections of the more-common Salmonella and Campylobacter can pose significant risks to the fetus, pregnant women don't appear to be more susceptible to those bugs. But they are to Listeria, and the reason may be a bit more complex than you think.
When a woman becomes pregnant, her body undergoes hormonal and immunological changes allowing her body to accept the fetus. Without those changes, the body's tendency would be to reject the baby and cause a miscarriage. That's because the fetus contains genetic material from the father as well as the mother, and the mother's immune system could mistake the fetus for a foreign object and try fight it off.
The adjustment in the mother's immune system involves suppressing a type of response called "cell-mediated immunity," while allowing another type of immune function (the type that involves antibodies) to remain functioning. Cell-mediated immunity is the kind involved in the rejection of organ transplants, but it's essential to control pathogens that move from cell to cell. One of those pathogens is Listeria monocytogenes.
Most food-borne pathogens attack the gastrointestinal system, but Listeria can move from the digestive tract into the bloodstream. With cell-mediated immunity restrained, Listeria infection can more easily take hold.
Pregnant women appear to be more susceptible to Listeria -- more than one-quarter of all listeriosis diagnoses occur in pregnant women, most during the third trimester when cell-mediated immunity is at its lowest ebb. Usually, listeriosis causes only mild symptoms in the adult, but early labor and delivery is common. Miscarriage and stillbirth are serious risks. Pregnant women can take steps to reduce their risk by avoiding foods usually associated with listeriosis. Those include:
- Soft cheeses, made with raw milk, such as camembert, brie, and Mexican-style such as Queso Fresco.
- Smoked fish that are "cold-smoked" (smoked at temperatures low enough to allow Listeria to survive), including those labeled nova-style, lox, kippered or jerky.
- Seafood salads, such as crab, imitation crab or shrimp salad.
- Lunch meats and hot dogs served and eaten without being warmed to steaming hot.
For more information, see the U.S. Food Safety and Inspection Service's fact sheet, "Protect Your Baby and Yourself From Listeriosis," at http://www.fsis.usda.gov/Fact_Sheets/Protect_Your_Baby/index.asp.
Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or firstname.lastname@example.org.
Editor: This column was reviewed by Lydia Medeiros, associate professor of human nutrition in the College of Education and Human Ecology, a state specialist with Ohio State University Extension, and a researcher with the Ohio Agricultural Research and Development Center.