PREVALENCE OF LATENT TOXOPLASMOSIS AND SEROLOGICAL DIAGNOSIS OF ACTIVE INFECTION IN HIV-POSITIVE PATIENTS

The seroprevalence of latent Toxoplasma gondii infection was determine d in a cohort of 715 HIV-positive patients followed up at an HIV outpa tient clinic. Using indirect immunofluorescence and direct agglutinati on assays for detecting IgG, the prevalence of anti-Toxoplasma gondii antibodies was shown to be 50 %. During a four-year period, clinically apparent acute toxoplasmosis occurred in 47 patients (43 with cerebra l, 3 with ocular and 1 with bone marrow toxoplasmosis) among the 360 p atients positive for anti-Toxoplasma gondii IgG and in one patient (wi th cerebral toxoplasmosis) among the 355 patients who were serological ly negative. A significant rise in IgG levels could be shown during ac ute toxoplasmosis episodes in only 30 % of patients, compared with 3 % of patients without active toxoplasmosis. During acute toxoplasmosis, IgM antibodies were detected in only two patients (6 %) by an immunos orbent agglutination assay and in one (3 %) by an enzymatic immunocapt ure assay. Specific IgA was detected by a non-enzymatic immunocapture assay in six patients (18 %) during acute episodes. The very high pred ictive value (99.7 %) of a negative IgG test remains the best serologi cal parameter for excluding an acute episode of toxoplasmosis in HIV-p ositive patients.