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Listeriosis During Pregnancy

Edited by: Mary Schroeder, M.S., R.D. & Pat Kendall, Ph.D., R.D., Colorado State - Fall 2003

The recent outbreak of listeriosis in south Texas, associated with consumption of queso fresco and involving six pregnant women and seven babies thus far, again highlights the importance of following safe food consumption and handling practices during pregnancy. In the Summer, 2003 issue of SafeFood News we talked about issues with toxoplasmosis during pregnancy. Listeria monocytogenes is another pathogen that can cause grave consequences during pregnancy, particularly for the unborn child.

Listeria monocytogenes is widely distributed in nature and can be found in soil, ground water, plants and animals. Most infections in humans, however, result from eating contaminated food. Listeria monocytogenes has the ability to survive refrigeration temperatures, food preservatives such as salt, and conditions with little or no oxygen. Foods commonly associated with listeriosis have an extended shelf life and are usually eaten without further cooking. Reported outbreaks have been traced back to foods such as coleslaw, Mexican-style soft cheeses like queso fresco, raw milk, pat, pork tongue, hot dogs, processed meats and deli salads. Other foods that are a concern for harboring L. monocytogenes include raw and smoked seafood and ready-to-eat foods that have not been reheated to proper temperatures.

Infection from L. monocytogenes typically occurs in individuals with a weakened immune system, including pregnant women. During pregnancy, hormonal changes occur that cause the immune system to be suppressed so that the fetus is not aborted. It is estimated that pregnant women have a 17 times higher risk of developing listeriosis from eating contaminated food than other healthy adults, and account of 27% of all reported cases of listeriosis. Once in the bloodstream, Listeria bacteria can travel to any site, but seem to have a preference for the central nervous system and the placenta. The fetus is also unusually prone to infection from L. monocytogenes, which can lead to miscarriage, stillbirth, or infection of the neonate and health problems for the baby following birth.

Symptoms may take a few days or even weeks to appear and can be mild to severe. In pregnant women, listeriosis may cause mild, flu-like symptoms with the sudden onset of fever, chills, muscle aches and sometimes diarrhea or an upset stomach. Some women may not have any symptoms. A blood test can be performed to determine if the onset of symptoms is caused by Listeria infection and if confirmed, the patient can then be treated with antibiotics.

To avoid infection from L. monocytogenes, pregnant women are advised to practice safe food handling procedures, such as storing all perishable foods at or below 40ºF and using perishable or ready-to-eat foods as soon as possible. If a perishable food cannot be eaten within 4 days, it is best to freeze it. Kitchen surfaces, cutting boards and utensils should be washed before and after food preparation (especially after contacting raw meat). Pregnant women are recommended to avoid consumption of soft cheeses such as queso fresco, Camembert and Brie, unpasteurized milk and foods make from unpasteurized milk, raw or undercooked meat, refrigerated smoked seafood, deli salads, and hot dogs, luncheon meats and deli meats that have not been properly reheated. Leftover foods should be reheated to 165ºF before eating.

Sources:

1. FDA/ USFA/ CDC. Draft Assessment of the Relative Risk to Public Health from Foodborne Listeria monoctyogenes Among Selected Categories of Ready-to-Eat Foods. 2001.
2. FSIS and USDA. "Listeriosis and Pregnancy: What is Your Risk?: Safe Food Handling for a Healthy Pregnancy," 2001.
3. Lorber B. Listeriosis. Clinical Infectious Diseases. 24(1): 1-11, 1997
4. Mylonakis E, Paliou M, Hohmann E, et al. Listeriosis During Pregnancy: A Case Series and Review of 222 Cases. Medicine. 81(4): 260-77,2002
5. Smith JL. Foodborne Infections During Pregnancy. Journal of Food Protection. 62(7): 818-829, 1999
6. Wing EJ and Gregory SH. Listeria monocytogenes: Clinical and Experimental Update. The Journal of Infectious Diseases. 185 (Suppl 1): S18-24, 2002



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