TOXOPLASMA SEROLOGY IN HIV-INFECTED PATIENTS - VALUE AND LIMITATIONS

Antibody titers to Toxoplasma gondii were studied in 62 AIDS patients with active toxoplasmosis (cerebral in 42, pulmonary in 10 and ocular in 10), confirmed by biopsy or by imaging techniques with a therapeutic test, and in 1 499 HIV-positive patients. The purpose of this study was to evaluate the value of antibody assays for the diagnosis of active infection and the prevalence of toxoplasmosis in HIV-positive individuals. IgG antibodies to Toxoplasma were found in 61 of the 62 AIDS patients, but not in one patient with pulmonary toxoplasmosis, with no significant differences in mean titers obtained by dye test, indirect immunofluorescence and sensitized agglutination. Twenty patients (31.7 %) had dye test titers of 400 IU/ml or more; three patients had IgM antibodies. Thirteen (38 %) of the 34 patients who had serial antibody assays exhibited a rise in IgG titers with no detectable production of IgM antibodies. Antibodies to Toxoplasma were found in 75 % of the 1 499 HIV-positive subjects, a proportion which is not significantly different from that seen in HIV-negative controls; however, HIV-positive subjects were significantly more likely than controls to have high titers (greater-than-or-equal-to 500 IU in 18.7 % of patients versus 9.2 % of controls, p < 0.001). A follow-up study in 177 HIV-positive patients with antibodies to Toxoplasma showed an annual reactivation rate of 12 %; in five of 30 patients, the rise in antibody titers occurred concomitantly with or a few months before clinical toxoplasmosis; 25 patients remained asymptomatic. These results show that the overall prevalence of toxoplasmosis is not greater in HIV-positive subjects than in controls but that high antibody titers and/or serologic reactivation may indicate clinical toxoplasmosis.