Concomitant cases of acquired toxoplasmosis in children of a single family: evidence of reinfection.

During 1979, three brothers had antibody titers for toxoplasmosis of 1:1,024, 1:64, and 1:16, respectively, by IgG indirect immunofluorescent antibody (IgG-IFA) test. The first child also had a fever and lymphadenopathy. In August 1980 the three children had lymphadenopathy and IgG-IFA test titers between 1:4,096 and 1:16,000. Two other brothers, first examined at that time, had IgG-IFA test titers between 1:1,024 and 1:4,096, one with ascending titers and the other with IgM antibodies to Toxoplasma gondii. The latter had lymphadenopathy, fever, and hepatosplenomegaly. Clinical and serologic examinations during March, April, and September 1981 revealed good health and decreasing IgG-IFA test titers in most of the brothers. The simultaneous increase of antibody titers during August 1980 in the three initial patients lead to the consideration of a probable reinfection. A simultaneous reactivation of the disease was considered less probable because acute toxoplasmosis occurred in two other brothers at the same time.