Current methods to establish the duration of toxoplasma infection in pregnant women and for the diagnosis of toxoplasmosis in the neonate or HIV infected patient have significant limitations. We assessed the precision of a commercial ELISA for the detection of toxoplasma specific IgG and adapted the assay to measure avidity using an elution agent washing step. The sensitivity and specificity of the ELISA were 100 and 75% respectively and optimal measurement of avidity was achieved using 6 M urea as the elution agent. Toxoplasma lymphadenopathy of less than 3 months duration was associated with low avidity specific IgG but some discordant findings were recorded. Serial measurement of IgG avidity assisted the distinction between actively produced antibody in infants with congenital toxoplasmosis and passively acquired antibody of maternal origin in uninfected babies. There was no significant difference between avidity levels in HIV infected patients with or without cerebral toxoplasmosis.

Summary, The microparticle capture enzyme immuno-assay (MEIA) is an automated system tor mea\uring specific antibody by interaction with antigen-coated particles. An MEIA rnethod for detecting tciroplasina-cpecific IgM was compared with established reference niethocls The MEIA had an acceptable level of sensitivity and reproducibility and was easier t o pcrforin t h a n con\entional tests. but it required expensive. dedicated equipment and, in our \tud!. false positive results were recorded with 7 '/o of samples. MEIA could be used to i n \ e\tigate imniunocompetent patients u ith suspected toxoplasmosis but positive findings should be corifirnied by an alternative form of assay. The technique is not suitable for the in\wtigation of neonates. for u hich a more sensithse method is required.