In Reply.—We appreciate Dr Frenkel's interest in our review article, and thank him for explaining the details of the direct agglutination test.
The lack of correlation between titers and the severity of the disease is a property shared by all conventional antibody tests. To avoid iteration we mentioned it only once, in association with the standard Toxoplasma antibody assay, the Sabin-Feldman test.
Underdiagnosis of congenital toxoplasmosis is the rule in children of all age groups. During the perinatal period, false-negative IgM results are common1-3 and the IgG antibodies may be either of maternal origin or due to intrauterine infection. Differentiation between these two conditions is thus far impossible. When IgG antibodies are detected in children over 6 months of age, differentiation between the acquired and congenital infection is also impossible, irrespective of the country. An "intelligently applied test" could, in principle, be exemplified by IgG antibody assays run