Incidence of HIV infection in a cohort of homosexually active men.

The purpose of this study was to estimate the incidence of human immunodeficiency virus (HIV) in a cohort of homosexually active men in Sydney. In 1984-85 the Sydney AIDS Prospective Study enrolled homosexually active men, who were followed by six-monthly visits, although regular contact with most participants ceased in the early 1990s. In 1993-94 a major effort was made to establish the HIV status of all participants who had attended more than once. Of the 1075 men enrolled, 528 (49 per cent) were negative at enrollment and had at least one further documented HIV test. The annual incidence rate of HIV infection was highest in the early years of the study, 1984 (9.6 per cent) and 1986 (5.0 per cent), and remained low from 1987 (1.9 per cent) to 1994 (0.0 per cent). The incidence of HIV infection was higher among men aged under 34 years at enrollment and men who reported more than four sexual partners in the six months before enrollment, but these associations disappeared by 1987. The decrease in HIV incidence is consistent with findings from other cohorts followed for this length of time.