You mean penetrating? I guess you mean being the penetrator and not the one being penetrated. Insertive anal sex is as risky with a man as with a woman, but no one quite knows even how risky insertive anal sex is anyway. Figures coming out of the gay community show that it does carry some risk, but it is far less risky than receptive anal sex. A friend of mine knows a gay man who says he did some research and now he has lots of gay sex with lots of men and he hasn’t gotten HIV yet. He said he only tops, and he never bottoms. He’s topped hundreds of gay men this way in recent years. Surely some of them were HIV positive.
There is at least one case in the porn world of a straight actor who got HIV from insertive sex on a porn set with some transsexual person or pre-op tranny or whatever the Hell it was. The actor got HIV from insertive anal with him/her/whatever.
There is another guy in porn who says he got it from a woman, but he doesn’t say how he got it.
Men are at risk of female-male HIV transmission in cases of penile and vaginal bleeding. The Padian Study in 1989 followed a number of HIV-serodiscordant heterosexual couples in which either the male or the female was HIV positive. Over a five year period through ~700 sex acts, 20% of the men had gotten HIV from their wives. This means that a man would have to have sex with an HIV positive woman 2,800 times in order to get HIV. Even after a man has sex with an HIV positive woman 40 times, he still only has a 1% chance of getting HIV. You have a 99% chance of not getting HIV even after having sex with an HIV positive woman 40 times for God’s sake!
In the Padian Study, female-male HIV transmission was highly correlated with episodes of vaginal and penile bleeding. Therefore it appears that the presence of blood during the sex act appears important in female-male HIV transmission. This makes sense as HIV is a blood-borne illness. Most people tend to forget that. Semen is only so transmissible because it is full of blood (little known fact).
I have studied titer levels needed to transmit HIV, and looking at HIV titers of HIV positive women in the US, I am a bit baffled at how it even transmits because the levels seem to low to transmit.
Vaginal titers are quite a bit higher in HIV positive prostitutes in Thailand and this makes sense as female-male transmission is happening a lot more over there. But even in Thailand, most female-male HIV transmission was found to be occurring due to vaginal bleeding in prostitutes servicing too many man a day. Even with that going on, the recent introduction of condoms reduced nearly eliminated that transmission. So condoms appear to be effective even in the presence of vaginal bleeding. This also makes sense if female-male HIV transmission is going via blood instead of vaginal fluid.
In addition, the urethra appears to be an inefficient vehicle to receive HIV. Anal and vaginal walls which may experience tiny tears are much better for transmission, especially the former. Anal walls are much more susceptible to tiny tears and microscopic bleeding than vaginal walls are, hence insertive anal sex would seem to put the insertive partner at greater risk due to increased chances of exposure to blood via the anus of the partner. This is probably the reason for the somewhat elevated risk from anal sex.