Age-specific HIV incidence among homosexually active men in Australia

Objective: To estimate age at HIV infection among homosexually active men in Australia. Design: Age-specific back-projection estimates of HIV incidence. Methods: Monthly counts of AIDS among homosexually active men diagnosed by 30 June 1994 and reported by 31 March 1995 were obtained from the National AIDS Registry and were adjusted for reporting delays. The progression rate to AIDS was estimated from a large cohort study of HIV-infected homosexual men, with adjustment for the effect of age at HIV infection and the effect of antiretroviral and prophylactic treatments. Results: The median age at HIV infection was estimated to have decreased from 31 years of age between 1982 and 1984 to between 23 and 27 years in the periods 1987 to 1989 and 1990 to 1994. Despite the trend to a younger median age at HIV infection during the current epidemic, HIV incidence was estimated to have declined in all age groups from a peak in the mid-1980s. This decline was more pronounced in the older age groups, with more modest reductions in age groups under 30 years. Conclusion: Most HIV infections among homosexually active men since 1987 appear to have occurred in men aged under 30 years. This has implications for education programs aimed at preventing HIV infection among homosexually active men.