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The purpose of this study was to characterize the epidemiologic, clinical, and laboratory parameters of a cohort of men at risk of AIDS-associated toxoplasmic encephalitis. One hundred seventeen (11%) of the 1,073 participants at the time of enrollment into the Chicago Multicenter AIDS Cohort Study (MACS) were seropositive for Toxoplasma antibodies. Significant differences in prevalence of antibodies between African-American, Hispanic, or white men were not observed (p = 0.49). One hundred one (86%) of the 117 antibody-positive participants had at least one follow-up serology performed and 6 (6%) of the 101 had a significant rise in IgG antibody titer on subsequent visits. Five of six participants with a significant rise in titer were also seropositive for HIV-1 at entry or seroconverted during the study. A trend toward higher IgG Toxoplasma titers and prevalence of IgM antibodies in participants seropositive for HIV-1 was observed, but the differences did not reach statistical significance. There was no evidence that the presence of Toxoplasma infection predisposed to development of CD4+ depletion or AIDS. None of the 183 individuals in the cohort who developed AIDS and who were seronegative for Toxoplasma antibodies developed toxoplasmic encephalitis. In contrast, of the 13 persons who developed AIDS and who were positive for Toxoplasma antibodies, 5 (38%) developed toxoplasmic encephalitis. Prevalence of Toxoplasma antibodies in the MACS population was independent of HIV-1 serostatus. Toxoplasma infection does not appear to predispose to progression of HIV-1 infection. The risk of development of toxoplasmic encephalitis in persons with AIDS and chronic Toxoplasma infection may have been underestimated by previous retrospective studies.

This study examines the risk of developing cytomegalovirus (CMV) retinitis as a function of the duration and degree of CD4+ lymphocyte depletion. A retrospective analysis of 135 persons infected with the human immunodeficiency virus (HIV) was performed. Kaplan-Meier estimates for the percentage of patients developing CMV retinitis during the 27-month study period were calculated. Twenty-six patients were diagnosed as having CMV retinitis. In 14 of these patients, T cell phenotyping was done within the 3 months preceding diagnosis. The mean CD4+ lymphocyte count for these patients was 15.6 cells/mm3 (range, 2-33/mm3). At 27 months, the percentage of patients developing CMV retinitis with baseline CD4+ lymphocyte counts of 0-50, 51-100, and 101-250 cells/mm3 was 41.9%, 26.3%, and 14.7%, respectively (log-rank test, p = 0.003). The odds ratio for developing CMV retinitis for those with baseline CD4+ lymphocyte counts of 0-50 cells/mm3 compared with those with CD4+ lymphocyte counts of 101-250 cells/mm3 was 4.62 (p = 0.002). Twenty-four patients had CD4+ lymphocyte counts of < or = 50 cells/mm3 for an average of 13.1 months prior to diagnosis. Twenty-two patients had an acquired immune deficiency syndrome (AIDS)-defining illness diagnosed for an average of 18.0 months prior to the onset of retinitis. CMV retinitis is most likely to develop in patients with AIDS when the CD4+ lymphocyte count is < or = 50 cells/mm3.