Congenital toxoplasmosis: a large survey in Western Australia

Abstract

To determine the birth prevalence of congenital toxoplasmosis in Western Australia. A prospective serological study of randomly selected pregnant women and their newborn infants. Paired sera collected from the mothers at their first antenatal visit and cord blood specimens taken from their infants were tested for toxoplasmosis by the direct agglutination test and Toxoplasma IgM-capture enzyme-linked immunosorbent assay. A major Perth metropolitan obstetric teaching hospital where approximately one-quarter of infants born in Western Australia during January 1986 to December 1989 inclusive were delivered. Sera were obtained from 10,207 pregnant women presenting for routine clinical evaluation at their first antenatal visit. Cord blood specimens were taken from 18,908 infants; 7523 of these could be paired to maternal specimens. Maternal infection was indicated in cases where Toxoplasma specific IgM antibody was present or where an initial maternal specimen gave negative results for Toxoplasma antibody but the paired cord blood specimen gave positive results. Toxoplasma specific IgM antibody in a cord blood specimen indicated fetal infection. Of the 10,207 women 3544 (35%) were Toxoplasma immune at their first antenatal visit; in 11 Toxoplasma specific IgM antibody was detected. There was no serological or clinical evidence of congenital toxoplasmosis in any of the offspring of these 11 mothers. The rate of maternal infection in susceptible pregnancies was 1.6 per 1000; the maternal-fetal transmission rate was estimated to be no greater than 24%. Three of the 18,908 cord blood specimens tested gave positive results for Toxoplasma specific IgM antibody giving a birth prevalence of congenital infection of 0.23 per 1000 births to non-immune mothers. There were no clinical features of congenital infection in these three infants but they will require long-term follow-up. Thirteen of the 14 mothers infected during pregnancy were interviewed retrospectively and in only three was a known risk factor for infection present. a toxoplasmosis screening programme for pregnant mothers is not justifiable in Western Australia. A public education programme is also likely to have limitations.