Toxoplasmosis in Pregnancy: Cook the Meat and Avoid Soil
August 15, 2000 4 minutes read
Toxoplasmosis in Pregnancy: Cook the Meat and Avoid Soil
abstract & commentary
Synopsis: Eating undercooked meat, contact with soil, and travel outside Europe, the United States, and Canada—but not contact with cats—are the major risk factors for acquiring acute toxoplasmosis during pregnancy.
Source: Cook AJC, et al. Sources of toxoplasma infection in pregnant women: European multicentre case-control study. BMJ 2000;321:142-147.
Cook and colleagues set out to determine the risk factors for the acquisition of Toxoplasma gondii infection during pregnancy. To this end, 252 women with serological evidence of toxoplasma infection during pregnancy and 858 control women were enrolled at five European centers: Naples, Lausanne, Copenhagen, Oslo, Brussels, and Milan. Data were collected by interview. After elimination of confounding factors, logistic regression analysis was performed.
Risk factors that were most strongly associated with the development of acute toxoplasmosis in pregnancy were eating undercooked lamb, beef, or game, contact with soil, and travel outside Europe, the United States, and Canada. Contact with cats was not a risk factor. Depending on the center, between 30-63% of infections were attributable to meat consumption, while 6-17% were attributable to soil contact.
Comment by Stan Deresinski, MD, FACP
While the risk for acquisition of toxoplasmosis is indelibly linked in my mind with cats, felines are only a small part of the story, as confirmed by study. Nonetheless, the risk posed by contact with soil is largely the result of toxoplasmosis in cats. Cats excrete large numbers of oocysts—but only during their initial infection and then for only approximately two weeks. The oocysts, however, may survive in moist soil for a year of more.
A previous case-control study performed in France, a country in which there are almost 5000 primary Toxoplasma infections in pregnancy each year, did find that having a pet cat, as well as poor hand hygiene, consumption of undercooked beef or lamb, and frequent consumption of raw vegetables outside the home, was a risk factor for acquisition of infection.1 Other studies, however, concur with the current one in finding that cat exposure was not a risk factor.2-4
In contrast, the association between acute infection with T. gondii and ingestion of raw or undercooked meat is a consistent finding among studies. Among meats, chicken is reported to be the least likely source. Freezing kills the cysts, but curing may not reliably do so.
The serological diagnosis of acute toxoplasmosis in pregnancy is not without difficulty, unless there is an opportunity to demonstrate seroconversion. One laboratory uses a large panel of tests in an attempt to overcome this difficulty: Sabin-Feldman dye test, ELISA (IgM, IgG, and IgE), IgE immunosorbent assay, and a differential agglutination test.5 A IgG avidity test may be of value.
Since infection of the woman does not inevitably lead to infection of the fetus, additional diagnostic measures must be taken. A recent study found that the combination of PCR for T. gondii DNA and mouse inoculation of amniotic fluid had a sensitivity of 91%, and a specificity of 96% in the prenatal diagnosis of congenital toxoplasmosis.6
Once acute infection in pregnancy is recognized, treatment is recommended, most commonly with spiramycin, in an attempt to prevent congenital infection.5 However, a recent Cochrane meta-analysis found that none of the 2591 published studies reviewed met their selection criteria, which included the presence of an adequate control group.7 As a result, it was concluded that the benefit of antenatal treatment remains unproven.
The optimal approach to the problem of congenital toxoplasmosis remains prevention. Cook et al conclude that, "Action to reduce infection rates should include improved information about the risk associated with undercooked or cured meat, labelling of meat according to farming and processing methods, and measures to reduce infection in domestic animals."
References
1. Baril L, et al. Risk factors for Toxoplasma infection in pregnancy: A case-control study in France. Scand J Infect Dis 1999;31:305-309.
2. Bobic B, et al. Risk factors for Toxoplasma infection in a reproductive age female population in the area of Belgrade, Yugoslavia. Eur J Epidemiol 1998;14:605-610.
3. Buffalano W, et al. Risk factors for recent toxoplasma infection in pregnant women in Naples. Epidemiol Infect 1996;116:347-351.
4. Kapperud G, et al. Tisk factors for Toxoplasma gondii infection in pregnancy. Results of a prospective case-control study in Norway. Am J Epidemiol 1996;144: 405-412.
5. Montoya J, Remington J. Toxoplasma gondii. In: GL Mandell, JE Bennett, Dolin R, eds. Principles and Practice of Infectious Diseases. 5th ed. Philadelphia, Pa: Churchill Livingstone; 2858-2888.
6. Foulon W, et al. Prenatal diagnosis of congenital toxoplasmosis: A multicenter evaluation of different diagnostic parameters. Am J Obstet Gynecol 1999;181:843-847.
7. Peyron F, et al. Treatments for toxoplasmosis in pregnancy. Cochrane Database Syst Rev 2000;(2): CD001684.
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