Cord blood screening for congenital toxoplasmosis in northwestern Switzerland, 1982-1999.

BACKGROUND

In the absence of mandatory nationwide toxoplasmosis screening during pregnancy in Switzerland, the Basel region introduced cord blood screening in 1982.

METHODS

From 1982 to 1999, 64,622 cord blood samples (>90% of all neonates) collected in Basel region obstetric units were screened for toxoplasma specific immunoglobulin (Ig) G, M and A antibodies using commercial kits. Neonates with relevant results (IgG titers > or =300 IU/mL, or > or =200 IU/mL in the Abbott Toxo IMX system, and/or positive IgM or IgA antibodies) were monitored until clarification of infection status. From 1991 onward, retrospective maternal and follow-up data on these children were also collected by questionnaire.

RESULTS

Despite increasing maternal age, seroprevalence for toxoplasmosis decreased steadily from 53% (1982-1985) to 35% (1999). During the same period, the prevalence of congenital toxoplasmosis declined from 0.08% to 0.012%. IgM and/or IgA antibodies were present with the Platelia Toxo test (enzyme-linked immunosorbent assay; sanofi pasteur; Bio-Rad) in the cord blood samples of 17 of 18 infected neonates born between 1986 and 1999, regardless of maternal treatment in pregnancy. Vertical transmission rates in 69 women with proven or suspected primary infection between 1991 and 1999 were 3.9% with, compared to 27.7% without, antiparasitic treatment during pregnancy.

CONCLUSION

Toxoplasma seroprevalence and congenital toxoplasmosis incidence declined markedly in northwestern Switzerland from 1982 to 1999. Our data provide no conclusive evidence that maternal antiparasitic therapy in pregnancy affects vertical transmission because the treatment group also included women with suspected but unproven primary infection during pregnancy. Because toxoplasma specific IgA/IgM antibodies in cord blood identified almost all infected children, screening at birth may be more cost effective than during pregnancy.