Toxoplasma gondii in eluates from Guthrie cards

Aims: To determine whether the Eiken particle agglutination test could be modified to make it sufficiently sensitive to screen blood samples collected on Guthrie cards for the presence of antibodies to Toxoplasma gondii; to evaluate the specificity of the modified system; and to compare seroepidemiological data on the prevalence ofTgondii in pregnant women. Methods: Simulated dried blood spots were prepared from sera from pregnant women booking for antenatal care. Eluates from the simulated dried blood spot cards and sera were tested in parallel using the modified test (1 in 5 dilution of latex) and the standard assay (neat latex particles) and endpoints determined. Guthrie card eluates, from neonates in three Thames regions, were then tested using the modified test. Results: The modified test produced a 4*21-fold increase in antibody titre in 85 sera when tested in parallel with the standard test. Eluates of 1681170 from simulated dried blood spots derived from seropositive patients gave a positive result in the modified test. The two eluates which gave a negative result were derived from patients with an equivocal titre of 1116 in the standard serum test. Of the eluates derived from serum negative patients all 103 were negative at a dilution of 1 in 4 in the modified test. The seroprevalence of antibodies to T gondii in pregnancy was 21-8% using the standard test. A similar value of 20-5% was obtained when dried blood spots from neonates in a similar region of London were tested by the modified test. Conclusions: The modified Eiken Toxoreagent test is sensitive, simple, and economic for screening large numbers of dried blood spots. The procedure could be easily semiautomated and the technique applied to the mass screening of neonatal blood samples collected on Guthrie cards to determine the seroprevalence ofTgondii in pregnant women. ( Clin Pathol 1992;45:907-909) It has been suggested recently that the true extent of problems associated with congenital toxoplasmosis infection are being overlooked. As a result, the proposed introduction of a programme for screening pregnant women in the United Kingdom has provoked controversy. The epidemiology of Toxoplasma gondii in women has been reviewed,'--' and serological studies have shown a wide variation in the prevalence of antibodies in European countries: France 80%4; Belgium 50%5; Netherlands 40%'; Finland 19%7; and England 19%.8 However, seroprevalence has fallen rapidly over the past 20 years in Sweden9 and in parts of England.'0 Inexpensive and effective methods of surveillance are reported to monitor changes in seroprevalence so that appropriate strategies to prevent infection can be implemented. Blood collected from neonates on Guthrie cards has been used for many years in the United Kingdom and the United States of America for screening for the presence of metabolic diseases." 12 Such samples have been used in the USA for seroepidemiology studies of the prevalence of antibodies to HIV1 in pregnant women. '3 '4To reduce the cost of neonatal screening in the United Kingdom the Fujirebio anti-HIV-1 particle agglutination assay was modified. " Its efficacy has been confirmed for the determination of the prevalence of maternal HIV-1 infection based on unlinked anonymous testing of neonates.'6' As a result of our experience with the modified HIV1 test, we decided to evaluate the use of the Toxoreagent latex agglutination test, which we modified in a similar way.