[Differences in HIV-risk behavior of bisexual men in their relationships with men and women]

To describe bisexual men's behavior in terms of sexual identity, condom use, frequency of sexual intercourse and types of partners and to determine rates of inconsistent condom according to partner's gender.

Cross-sectional study nested in a cohort of HIV-negative homosexual and bisexual men in the city of Belo Horizonte, Southeastern Brazil, followed up since 1994 (Horizonte Project). Of 1,025 subjects enrolled between 1994 and 2005, 195 volunteers who reported at admission having sexual relations with men and women during the previous six months were selected. A behavioral risk index, called Horizonte Risk Index, was estimated. It incorporates a constant assigned to each type of unprotected sexual act, adjusted for the number of sexual encounters.

Sexual activity with men predominated; most considered themselves as bisexual (55%) and homosexual (26%). During the six months prior to the study, median number of casual male partners (4) was higher than both casual female partners (2) and steady male or female partners (1). During vaginal sex with a steady partner, the rate of inconsistent condom use was 55%, compared to 35% and 55% in anal insertive and anal receptive sex, respectively, with steady male partners. The index was higher for those having sex with men and women compared to those having sex either exclusively with women or men (p=0.004).

HIV risk behavior was more frequent among men who reported sexual activity both with men and women. Bisexual men display different sexual and protective behavior according to gender and steadiness of relationships, and female steady partners had more unprotected encounters.