Comparison of sexual behaviors, unprotected sex, and substance use between two independent cohorts of gay and bisexual men

FRANÇAIS :
Les deux cohortes comparées sont : 235 hommes séronégatifs au VIH qui ont participés au Vanguard Project (VP) de mai 1995 à avril 1996 et 263 hommes séronégatifs qui ont participés à la Vancouver Lymphadenopathy AIDS Study (VLAS) de janvier à décembre 1985. Après contrôle des différences liées à l'âge, à l'ethnie, à la consommation de drogues, et à la méthode de recrutement entre les 2 cohortes, les résultats montrent que les participants à l'étude VLAS sont 9 fois plus susceptibles d'avoir un comportement sexuel à haut risque ; leur risque de séroconversion est significativement plus élevé que celui des participants au VP. Les participants au VP rapportent plus d'usage de cocaïne (30 vs. 8%), de LSD (21 vs. 3%), d'amphétamines (11 vs. 1%), d'héroïne (3 vs. 0%) et de méthyldiamphétamines (11 vs 1%) et montrent une activité sexuelle (évaluée par le nombre de partenaires réguliers et occasionnels et par la fréquence de rapports anaux) très supérieure à celle, 10 ans auparavant, des participants à la VLAS. Cependant, un usage de préservatifs qui semble significativement supérieur chez les participants au VP a contribué à une plus faible contamination par le VIH-1 de cette cohorte.
ENGLISH :
Objective: To compare demographic characteristics, sexual practices, unprotected receptive and insertive anal intercourse, substance use and rates of HIV-1 seroconversion between two prospective cohorts of HIV-negative men who have sex with men. Design: Comparative analysis of two independent cohorts. Methods: Between May 1995 and April 1996, 235 HIV-negative Vanguard Project (VP) participants were enrolled and between January and December 1985, 263 HIV- negative participants in the Vancouver Lymphadenopathy AIDS Study (VLAS) completed a follow-up visit. The VP participants were compared with VLAS participants with respect to self-reported demographic variables, sexual behaviors, unprotected sex, substance use and rates of HIV-1 seroconversion during follow-up. Results: In comparison with the VLAS participants the VP participants were younger (median age, 26 versus 34 years; P < 0.001), more likely to be non-Caucasian (75 versus 97%; P< 0.001), and were less likely to have attended university/college (35 versus 46%; P = 0.014). The VP participants reported a higher mean number of male sex partners in the previous year (15 versus 12; P = 0.026) and a higher mean number of regular partners (1.7 versus 0.6; P < 0.001). The VP participants were more likely to report engaging in receptive (92 versus 60%; P < 0.001) and insertive (90 versus 69%; P < 0.001) anal intercourse with regular partners and receptive anal intercourse with casual partners (62 versus 38%; P < 0.001). The VLAS participants were more likely to report never using condoms during insertive and receptive anal intercourse with both regular and casual partners. The VP participants were less likely to report using nitrite inhalants (34 versus 43%; P= 0.033), but more likely to report the use of cocaine (30 versus 8%; P < 0.001), LSD (21 versus 3%; P < 0.001), amphetamine (11 versus 1%; P < 0.001), heroin (3 versus 0%; P = 0.010) and methyldiamphetamine (17 versus 10%; P = 0.034). The VLAS participants were nine times more likely to report high-risk sexual behavior, after controlling for differences in age, ethnicity, substance use, and method of recruitment between cohort members. After adjustment for differences in demographics, sexual behaviors, and level of substance use, the risk ratio for seroconversion among VLAS participants remained significantly elevated compared with VP participants. (Author' s abstract)