Rectal secretions

Very little research addresses this topic, but a study from the University of Washington, Seattle, found that levels of HIV RNA in rectal mucosal secretions in gay men were higher than those in blood or semen – by about 500% in the case of blood and 2500% in the case of semen.¹

The study found that viral loads in swabs taken from the rectum were 25 times higher than semen viral loads in the 58% of the men not taking HIV treatment, and four times higher in the 37% of men on treatment who had detectable viral loads.

The average rectal viral loads were 316,000 and 4000 respectively.

There was also a much less strong relationship between the use of treatment and reduction of viral load in the rectal swabs than there was with blood or semen.

Previous studies of HIV RNA in rectal tissues had used biopsy specimens, and HIV was very frequently detected. However biopsies may not represent the quantity of HIV in rectal secretions which insertive sexual partners are exposed to. One other study² used anal swabs, which would sample the anal canal, rather than towards the top of the rectum, as in the University of Washington study.

Another study from the same team at Washington found that men with herpes simplex shedding in the rectum had higher HIV RNA levels, in both rectal swabs and blood plasma.³

During anal intercourse, the rectum secretes a protective, lubricating mucus that accommodates penetration. Although the mucus eases penetration and repeated thrusting, it by no means protects either partner from cuts and abrasions that can increase the risk of HIV transmission, which is why proper lubrication and condom use is necessary. In fact, the mucus may be far more infectious than any other fluids either partner might be exposed to.

The study suggests that men who have insertive unprotected anal sex and encounter this mucus are at far higher risk of HIV infection than had been previously thought. Formerly, most literature on HIV protection named blood or semen as the main culprit in HIV transmission.