Since the beginning of the HIV epidemic in north America, the majority of HIV infections have occurred among men who engage in sexual relations with other men. As the HIV epidemic enters its third decade, gay and bisexual men continue to have among the highest rates of HIV infection. Previous studies [1,2] have highlighted the decline in the incidence of HIV and risk behaviour among gay and bisexual men. However, several studies [3,4] have suggested that young gay and bisexual men continue to engage in unprotected sexual behaviours and are at continued risk of HIV infection. Recent reports in the media [5–9] and research literature [10,11] have indicated an increase in the incidence of HIV among gay and bisexual individuals in many of the world's major cities. The purpose of this study was to determine trends in HIV incidence using data from a prospective cohort of young gay and bisexual men.
The Vanguard Project is a prospective study of gay and bisexual men aged 15–30 years, living in the greater Vancouver region. These men were recruited through outreach, clinics, and physicians’ offices. To be eligible for this longitudinal study, the participants must have not previously tested positive for HIV and must have self-identified as gay or bisexual or have had sex with other men. Vanguard participants have completed a self-administered questionnaire and undergone HIV antibody testing on an annual basis since May 1995.
The incidence of HIV was calculated per annum as the number of new infections divided by the total person-time under observation for each calendar year from study inception to December 2000. Person-time was calculated as the interval between enrolment and the most recent follow-up visit for individuals who did not seroconvert. For individuals who became HIV positive, person-time was calculated as the interval between enrolment and the first visit at which an HIV-positive test result was detected. Ninety-five per cent confidence intervals (CI) for the incidence estimates were calculated on the basis of Poisson distribution.
As of 31 December 2000, 668 men had completed at least one questionnaire and two HIV tests. Table 1 provides a summary of HIV incidence in the cohort by year since its inception in 1995. As shown here 26 HIV infections were prospectively observed over the follow-up period (mean follow-up 2.87 years), resulting in an overall incidence rate of 1.4 per 100 person-years (PY; 95% CI 0.8–1.9). Among participants who reported injection drug use, the incidence rate was higher (3.9/100 PY) than among those participants who did not report the use of injection drugs (1.0/100 PY). A significant increase in new HIV infections was observed between 1995–1999 and 2000 within the entire cohort. This remained true when participants who had injected drugs were excluded from the analysis (P < 0.05). Among men who had never injected drugs, the rate of new infections increased from 0.6 per 100 PY in 1995–99 (95% CI 0.2–1.0) to 3.7 per 100 PY in the year 2000 (95% CI 1.0–6.5).
The observed increase in incidence in our cohort corroborates previous reports from other major cities [6–12]. Furthermore, the upturn in the incidence of HIV is consistent with increased rates of rectal gonorrhea and sexual risk behaviour reported among gay and bisexual men . Overall, such studies suggest the need for continued vigilant surveillance and further investigation of the determinants of seroconversion, in order to assist with the efforts to stabilize or decrease seroincidence in this population of men.
Robert S. Hogga
Amy E. Webera
Mary Lou Millera
Kevin J. P. Craiba
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