Nonetheless, many of the studies were carried out before antiretroviral treatment after diagnosis became the norm and so are likely to over-estimate the risk of infection.
The most recent review of the evidence estimated that for each condomless act with an HIV-positive partner, the risk of infection was 1.38% (one in 72 chance) for the receptive partner and 0.11% (one in 909 chance) for the insertive partner (Patel). Receptive anal intercourse refers to the act of being penetrated during anal intercourse. Several systematic reviews of studies have calculated that condomless receptive anal intercourse posed approximately ten to twelve times greater risk of infection than insertive anal intercourse. This creates a risk of transmission to the insertive partner through the tissue in the urethra and on the head of the penis – particularly underneath the foreskin. The insertive partner (‘top’) is also at risk of infection, as there are high levels of HIV in rectal secretions, as well as blood from the rectal tissues (Zuckerman). However, such tissue damage is not necessary for infection to occur: the rectal tissue itself is rich in cells which are directly susceptible to infection. Rectal tissue is delicate and easily damaged, which can give the virus direct access to the bloodstream. The receptive partner (‘bottom’) is at risk of infection from HIV in the semen and pre-seminal fluids ('pre-cum') of the infected partner. The per-act risk for the insertive partner in anal sex is comparable to the per-act risk for the male (insertive) partner in vaginal sex. However, being the insertive partner in condomless sex remains a high-risk activity. It is true that HIV infection occurs less frequently in men who solely take the insertive role than in men who engage in both roles, or men who practise receptive anal intercourse only (Jin). There is a widespread belief among gay men that the insertive partner (‘top’) is at very low risk of HIV infection. Risks to insertive and receptive partners Studies have identified several other factors that further increase the risk of transmission. However, it may be 10 to 25 times higher if the positive partner is recently infected. The latest news and research on sexual transmissionįor each condomless act with an untreated HIV-positive partner, the risk of infection has been estimated at 1.38% (one in 72 chance) and 0.11% (one in 909 chance) for the receptive and insertive partners respectively. If viral load is detectable, condomless anal intercourse is a highly efficient way of transmitting HIV, and it is considered a high-risk activity for both partners, although the exact degree of risk can depend on many factors.
After 1596 couple-years of follow-up and 77,000 acts of unprotected anal intercourse, no HIV transmission from HIV-positive partners took place and the researchers concluded that the risk of HIV transmission in these circumstances was effectively zero (Rodger). The PARTNER-2 study followed 783 male couples in which the HIV-positive partner had an undetectable viral load and no condoms were used in anal intercourse. If the HIV-positive partner is taking antiretroviral treatment and has a fully suppressed viral load (‘undetectable’), the risk of HIV transmission through anal intercourse is zero.