Incidence of toxoplasmosis in pregnant women in the city of Malmö, Sweden.

The incidences of latent and primary Toxoplasma gondii infections in pregnant women were studied using stored sera from 4,351 women delivered in the city of Malmö, Sweden in 1982 and 1983. Infants born to mothers with signs of primary infection (seroconversion or specific IgM in sera collected during pregnancy) were studied with regard to serological evidence of congenital infection (specific IgM in cord serum). Sera were tested for specific IgG antibodies by direct agglutination test and enzyme-linked immunosorbent assay, and for specific IgM by immunosorbent assay. 40% of the women were seropositive at delivery. Seroconversion (change from negative to positive serological status) was demonstrated in 12 pregnant women and specific IgM in the first postconceptional serum sample (indicating infection in the first trimester or in the last year(s) before conception) in another 17. The incidence of primary maternal infection was calculated to 4-6:1,000 deliveries. Among the 29 infants born to mothers with seroconversion or, alternatively, IgM in the first postconceptional sample, 6 had laboratory signs of congenital infection. One of the 6 had a positive toxoplasma isolation test in autopsy material and 5 had a clearly positive IgM value in cord serum. The real incidence of congenital infection in this material is unknown since IgM might be absent or sparse in cord serum in spite of congenital infection. The noticeable prevalence of maternal toxoplasmosis in Malmö calls for further incidence studies in Sweden.