via Aidsmap, by Roger Pebody

“It may be possible that HIV transmission by anal intercourse is not as closely related to viral load as it is in vaginal transmission. There is a paucity of data on HIV transmission at low viral loads, and there are almost no data on transmission and viral load in homosexual men.”

Although the widespread use of antiretroviral therapy could be expected to make HIV-positive gay men less likely to pass on HIV during unprotected sex than in the early 1990s, the risk of transmission per-sexual-act is actually quite similar, Australian researchers report in AIDS.

The authors put forward a number of suggestions to explain this surprising finding – that transmission during primary infection is a more significant factor than before 1996, that sexually transmitted infections are now more common, or that viral load is a less important factor for anal transmission than for vaginal transmission.

Their study also suggests that circumcised men who have unprotected insertive sex are less likely to acquire HIV than men who are not circumcised, and that ejaculation inside the rectum increases the risk of transmission during unprotected receptive anal intercourse.