Oral sex cannot be linked to new HIV infection in 10 year Spanish couples study

Over 19,000 instances of unprotected oral sex did not lead to a single case of HIV transmission amongst a cohort of 135 HIV-negative Spanish heterosexuals in a sexual relationship with a person with HIV. The study, conducted between 1990 and June 2000, is reported in the June 2002 edition of AIDS and adds to the growing number of studies which suggest differing levels of risk of HIV transmission from oral sex when compared to anal or vaginal intercourse.

A research team at the sexually transmitted diseases and HIV testing clinic in Madrid monitored a cohort of HIV-negative heterosexuals in a “steady” sexual relationship with a person with HIV. Both members of the couple were monitored at the clinic every six months and the HIV-negative partner was tested for HIV. Both members of the couple were asked to complete a structured questionnaire about their sexual practices and other possible exposures to HIV. The questionnaire explicitly asked people to specify each type of sexual practice since their last clinic visit and an approximate weekly and monthly frequency of each type of sexual activity was calculated by the researchers from their answers. A distinction was made between unprotected and protected sex and people were also asked whether ejaculation occurred.

In total, 135 HIV-negative people (110 women and 25 men) were recruited to the study. Of the women, 96 had performed fellatio on their HIV-positive partner, giving an estimated total of 8,965 instances of unprotected fellatio, with ejaculation occurring in the mouth on an estimated 3,060 occasions (34%). Ninety-eight HIV-positive men carried out unprotected cunnilingus on their HIV-negative partner.

Amongst the 25 HIV-negative men with a positive partner, 12 had unprotected cunnilingus, with an estimated 614 total number of episodes. Twenty-four of the 25 men had passive fellatio, with a total of 1,081 instances of fellatio without a condom performed by the HIV-positive partner.

It is thought that certain factors increase the chances of passing on HIV through oral sex. These include the HIV-positive person having a high viral load. In the Madrid study, viral load results were only available for 60 members of the cohort. Of these 10% (6) had a viral load above 10,000 copies/ml. CD4 counts below 200 cells/mm³ were recorded in 15.6% of the HIV-positive people in the study.

Other risk factors include the HIV-positive person ejaculating into the mouth of their partner; the presence of an sexually transmitted infection; and poor oral health. Amongst the HIV-positive men, 34% ejaculated into the mouths of their partners and vaginal infections were detected in two of the HIV-positive women who had cunnilingus performed on them by a HIV-negative partner.

In total almost 19,000 instances of unprotected oral sex were estimated to have occurred involving the 135 couples over the ten years of the study, but not a single case of HIV transmission was detected. The study authors conclude that: “this seems to point to a very low probability of HIV transmission related to this practice.”