HIV-affected people taking medication are highly unlikely to transmit the virus to their partners, even if they have unprotected sex, suggests new research. The risk is especially low for straight couples, according to the study.
For the study, published in the Journal of the American Medical Association (JAMA), the researchers followed 900 straight and gay couples.
The couples were sero-different, meaning that one partner was HIV-positive, while the other was HIV-negative. The HIV-positive partner was on suppressive anti-retroviral therapy and also reported condom-less sex.
Findings show that during a median follow up of 1.3 years per couple, there were no documented cases of within-couple HIV transmission.
The researchers however noted that appreciable levels of HIV transmission risk cannot be excluded, particularly for anal sex, and when considered from the perspective of a cumulative risk over several years.
"Although these results cannot directly provide an answer to the question of whether it is safe for sero-different couples to practise condom-less sex, this study provides informative data (especially for heterosexuals) on which couples could base their personal acceptability of risk," researchers say.
The study was conducted at 75 clinical sites in 14 European countries between September 2010 and May 2014.
Alison Rodger from University College of London along with her colleagues evaluated the rate of within-couple HIV transmission during periods of sex without condoms and when the HIV-positive partner had HIV-1 RNA load less than 200 copies/ml.
At study entry, couples reported condom-less sex for a median of two years.
Condom-less sex with other partners was reported by 108 HIV-negative men who had sex with men (33 per cent) and 21 heterosexuals (four per cent).
During follow-up, couples reported condom-less sex a median of 37 times per year, with men who have sex with men (MSM) couples reporting approximately 22,000 condom-less sex acts and heterosexuals approximately 36,000.
Although 11 HIV-negative partners became HIV-positive (10 gay, one straight) eight of them reported condom-less sex with other partners.
According to the study, no molecular characteristics-linked transmissions occurred over two years of follow-up, giving a rate of within-couple HIV transmission of zero.