Acquired immunodeficiency syndrome (AIDS)-free time after human immunodeficiency virus type 1 (HIV-1) seroconversion in homosexual men. Multicenter AIDS Cohort Study Group.

To estimate the time interval between human immunodeficiency virus type 1 (HIV-1) seroconversion and acquired immunodeficiency syndrome (AIDS) diagnosis in homosexual men, prospective incident cohorts are difficult to obtain and, if assembled, provide few events owing to the long incubation time. Although seroprevalent cohorts are numerous in size and events, the information is limited due to the unknown times since seroconversion. To combine the information provided by 1,628 seroprevalent men (304 AIDS cases) and 233 seroconverters (12 AIDS cases) being followed in a multicenter study since 1984, the postseroconversion changes in hematologic variables occurring in the incident cohort were used to develop a model that allowed for the imputation of the unknown times since seroconversion for the seroprevalent cohort. Nonparametric life table methods incorporating truncation and censoring were applied for the estimation of the probability distribution of the AIDS-free time after seroconversion. The precision of the estimates was evaluated using bootstrap methods. The analysis suggested that AIDS is unlikely (less than 0.5%) in the first year; 78% of seropositive homosexual men remain AIDS-free 60 months after seroconversion; and the AIDS incidence increases for months 12-36 and levels off at 38 per 1,000 person-semesters for months 42-60. The nonparametric estimate of the incidence rate suggests a median AIDS-free time of 11 years, which is longer than previous estimates based on parametric models.