[Congenital toxoplasmosis in Switzerland. Seroprevalence, risk factors and recommendations for prevention].

In 10,000 cord blood samples from the region of Basel (representing approximately equal to 42% of all live births of 1983 to 1985) anti-Toxoplasma antibodies were determined by agglutination and indirect immunofluorescence (IFA) tests. 47.3% were seronegative. 2.8% (n = 283) exhibited high titers in IFA (greater than 300 IU/ml) suggestive of acute or persistent infection. Questionnaires on potential risk factors were sent to 280 mothers with high antibody titers ("cases"), and to 279 randomised seronegative mothers (controls); 388 questionnaires (75.3%) were returned. Compared to controls, infections in cases were significantly associated with farm work, flower production, or food industry, consumption of lamb meat or improperly heated beefsteak, cat ownership. Risks of infection were significantly reduced when meat was kept in the deep freezer, or by consumption of chicken (probably as a surrogate for lamb and beef meat). Cases had significantly lower average serum concentrations of beta-carotene and tocopherol than controls, while average retinol and cholesterol levels were comparable in both groups. The 283 cord blood samples from the cases were subjected to 4 serological tests for specific IgM and 41 samples were reactive in greater than or equal to 1 test. 35 of the 41 children were reinvestigated greater than or equal to 6 months after delivery. In 8 children specific IgM persisted. Review of delivery charts confirmed that all 8 were asymptomatic at the time of delivery. Also on follow-up clinical examinations were normal. The incidence of congenital, latent toxoplasmosis in the area is thus estimated to nearly 1/1000 live births. These data will be used to promote preventive measures in pregnant women.