HIV infection and risk behaviours among young gay and bisexual men in Vancouver.

BACKGROUND Young gay and bisexual men may perceive that the consequences of HIV infection have dramatically improved with the availability of highly active antiretroviral therapy. We therefore sought to identify trends in HIV infection rates and associated risk behaviours among young gay and bisexual men in Vancouver. METHODS Prospective cohort study involving gay and bisexual men aged 18-30 years who had not previously tested HIV positive. Subjects were recruited through physicians, clinics and community outreach in Vancouver. Annually participants were tested for HIV antibodies and asked to complete a self-administered questionnaire pertaining to sociodemographic characteristics, sexual behaviours and substance use. Prevalence of HIV infection and risk behaviours were determined for eligible participants who completed a baseline questionnaire and HIV testing as of May 1998. The primary outcome was the proportion of men who reported having protected sex during the year before enrollment and who reported any episode of unprotected sex by the time of the first follow-up visit. RESULTS A total of 681 men completed a baseline questionnaire and HIV testing as of May 1998. The median duration between baseline and the first follow-up visit was 14 months. The median age was 25 years. Most of the subjects were white and of high socioeconomic status. The majority (549 [80.6%]) reported having sex only with men; 81 (11.9%) reported bisexual activity. Of the 503 men who had one or more regular male partners, 245 (48.7%) reported at least one episode of unprotected anal sex in the year before enrollment; the corresponding number among the 537 who had one or more casual male partners was 140 (26.1%). The prevalence and incidence of HIV seropositivity were 1.8% (95% confidence interval [CI] 0.8%-2.8%) and 1.7 per 100 person-years [95% CI 0.7-2.7], respectively. Fifty-two (26.5%) of the 196 and 55 (29.7%) of the 185 men with regular partners who reported having practiced protected insertive and receptive anal sex in the year before the baseline visit reported engaging in these activities without a condom at the follow-up visit; the corresponding numbers among the 232 and 242 men with causal partners who had practiced protected insertive and receptive anal sex before the baseline visit were 43 (15.5%) and 26 (9.4%) respectively at follow-up. INTERPRETATION The incidence of HIV infection is unacceptably high among this cohort of young gay and bisexual men. Preliminary results suggest a disturbing trend toward increasing levels of unprotected anal intercourse.