Elsevier

The Lancet

Volume 353, Issue 9167, 29 May 1999, Pages 1834-1837
The Lancet

Articles
Feasibility of neonatal screening for toxoplasma infection in the absence of prenatal treatment

https://doi.org/10.1016/S0140-6736(98)11281-3Get rights and content

Summary

Background

The best method for prevention and control of congenital toxoplasma infection is uncertain. Prenatal screening is done in Austria and France, but the effect of treatment during pregnancy is not well documented. The aim of our study was to find out the maternofetal transmission rate and outcome in infants born to mothers who were not treated during pregnancy.

Methods

We analysed 89 873 eluates from phenylketonuria (PKU) cards from neonates and paired first-trimester serum samples from the mothers for specific IgG antibodies to Toxoplasma gondii. Children born to mothers who seroconverted during pregnancy were followed-up clinically and serologically to 12 months of age. In addition, 21 144 PKU cards were analysed for toxoplasma-specific IgM antibodies during the last 12 months of the study.

Findings

In 24 989 (27·8%) cases both the PKU eluate and the first-trimester samples were IgG positive, which indicates previous maternal infection. 139 of the 64 884 seronegative women acquired toxoplasma infection during pregnancy and gave birth to 141 infants (two sets of twins). 27 of these children were diagnosed with congenital toxoplasma infection. The transmission rate was 19·4% (95% CI 13·2–27·0). Clinical signs and symptoms were found in four (15%) of the 27 children. The additional analysis for toxoplasma-specific IgM antibodies from the PKU card identifed seven of nine children with congenital toxoplasma infection. The false-positive rate for the IgM test was 0·19 per 1000, and no false-negatives were found.

Interpretation

The risks of transmission of infection and of disease in the infant are low in an area with a low risk of toxoplasma infection. A neonatal screening programme based on detection of toxoplasma-specific IgM antibodies alone will identify between 70% and 80% of cases of congenital toxoplasmosis.

Introduction

Infection with Toxoplasma gondii occurs worldwide.1 Fetal infection with T gondii may result in severe congenital defects like hydrocephalus, mental retardation, and retinochoroiditis, which may be present at birth or develop later in life. Early treatment is believed to prevent late-onset sequelae.2, 3, 4

The best approach to prevention and control of congenital toxoplasma infection is not clear. Some studies recommend health education alone,5 whereas in Austria and France, prenatal screening and treatment are carried out.6, 7 Studies showing the beneficial effect of prenatal screening were, however, done more than 30 years ago, when most pregnant women were immune and the incidence of infection in seronegative women was ten to 20 times higher than it is now.8, 9, 10 Since then, the seroprevalence in most countries had declined,11, 12 and the majority of pregnant women are seronegative and have a low risk of infection. The benefit of prenatal screening should therefore be balanced against the risk of side-effects from invasive diagnosis and treatment.

In this situation, neonatal screening seems an attractive and cost-effective alternative to prenatal screening or to health education alone. Neonatal-screening programmes for congenital toxoplasmosis have so far been rejected in Europe, since this approach means that infected women do not receive treatment during pregnancy. However, such screening had been used in New England, USA, for a decade.13

The study from New England showed that neonatal screening for congenital toxoplasma infection was feasible in a low-risk situation, based on analysis of toxoplasma-specific IgM antibodies eluted from the phenylketonuria (PKU) card.13 However, the study could not identify congenital infection with toxoplasma in IgM-negative neonates, and there is uncertainty about the number of toxoplasma-infected children not identified by the study.

Our study primarily aimed to find out the birth prevalence of congenital toxoplasma infection in live neonates, the maternofetal transmission rate in untreated, infected pregnancies, and the risk of clinical sequelae in children born to untreated mothers. The second aim was to assess the feasibility and acceptability of a neonatal screening programme based on detection of toxoplasma-specific IgM antibodies eluted from the PKU card.

Section snippets

Patients

Pregnant women from five counties in Denmark who gave birth to live infants were offered screening at delivery for primary toxoplasma infection during pregnancy; this population is about a third of all deliveries in Denmark. The study period was 51 months (June 1, 1992, to Aug 31, 1996), and all infants of seroconverted mothers were followed up for 12 months after birth.

Design and procedures

First-trimester serum samples (routinely taken for syphilis testing) were obtained from pregnant women betwen weeks 8 to 12 of

Results

During the 51-month study period 99 246 PKU cards from consecutive liveborn infants were received. 179 (0·18%) mothers refused to take part in the study. The first-trimester sample was missing from 9194 (9·26%) mothers, mainly because the first-trimester sample for syphilis is no longer mandatory, and their infants were excluded from the analysis. Infants from 89 873 mothers were included in the final analysis. Toxoplasma-specific IgG antibodies were detected in 24 989 of 89 873 PKU cards

Discussion

We found that there was a low risk of maternofetal transmission in women with untreated toxoplasma infection during pregnancy, and a low risk of substantial clinical signs in liveborn children with congenital toxoplasma infection. Maternofetal transmission rates for untreated pregnancies have been quoted at 15% in the first trimester, 25% in the second trimester, and 65% or more in the third trimester.8 Studies of treated women have reported lower transmission rates than these quoted rates from

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