A recent article on Science Daily, “Different HIV Rates among Gay Men and Straight People not fully explained by Sexual Behavior,” discusses recent research pertaining to the continued disparity of rates of HIV infection when comparing gay men (really "men who have sex with men," regardless of whether gay-identified or not) with heterosexuals in the U.S. For example, though a much lower proportion than in the 1980s and early 1990s, men who have sex with men still comprise just over half of new HIV infections in the U.S.
What’s interesting about the research reported on is that it doesn’t attribute the difference in infection rates to different rates of unprotected sex. In fact the research indicates roughly comparable rates of unprotected sex and numbers of partners for unprotected sex by homosexual men and heterosexuals. (I emphasize unprotected because there’s no given comparison for total numbers of partners for protected or unprotected sex. Given what I know of the gay community, I’d also find it hard to believe that the total number of partners per year is comparable for homosexual men and heterosexuals on average, even if the average number of partners for gay men is likely far down from the pre-AIDS heyday of the bath house scene.)
Instead, the research emphasizes different rates of infection for unprotected receptive anal versus vaginal intercourse (in itself, not particularly new news) and what they refer to as “role versatility.” Because many gay men practice both inserting and receptive roles in anal intercourse, it’s easy for gay men to become infected, especially through the receptive position, but also to pass it on to other men, especially when practicing the inserting position. Obviously, there is no analogous situation for heterosexuals, whether practicing vaginal or anal intercourse.
One thing the research doesn’t seem to take into account is the higher baseline infection rate for men who have sex with men. For men who have sex with men, the reality is that any given sex partner is more likely to be HIV-positive than is the case for heterosexuals. My own experience researching HIV prevention has indicated that in the community I studied, gay-identified men were much more knowledgeable of HIV prevention than others and much more likely to take safer sex practices seriously (even if this doesn’t mean they always practiced safer sex), but in cases where individuals did have unprotected sex, the chances that they did so with an HIV-positive individual were much higher than the corresponding chances for heterosexuals.