The study was conducted at 75 clinical sites in 14 European countries. (Representational image)
HIV-positive individuals undergoing treatment are not likely to transmit the deadly virus to their partner, even if they engage in unprotected sex, a new study has found.
Researchers followed nearly 900 couples - heterosexual and men who have sex with men (MSM) - in which one partner is HIV-positive, and was undergoing supressive antiretroviral therapy (ART).
During a median follow-up of 1.3 years per couple, there were no documented cases of within-couple HIV transmission, even in those who reported condomless sex, researchers said.
A key factor in assessing the effectiveness and cost-effectiveness of ART as a prevention strategy is the absolute risk of HIV transmission through condomless sex with suppressed HIV-1 RNA viral load for both anal and vaginal sex.
Researchers including Alison J Rodger, of University College London in the UK evaluated the rate of within-couple HIV transmission (heterosexual and MSM) during periods of sex without condoms and when the HIV-positive partner had HIV-1 RNA load less than 200 copies per ml.
The study was conducted at 75 clinical sites in 14 European countries and enrolled 1,166 HIV serodifferent couples (where one partner was HIV-positive).
Among the 1,166 enrolled couples, 888 (62 per cent heterosexual, 38 per cent MSM) provided 1,238 eligible couple-years of follow-up (median follow-up, 1.3 years).
At study entry, couples reported condomless sex for a median of 2 years. Condomless sex with other partners was reported by 108 HIV-negative MSM (33 per cent) and 21 heterosexuals (4 per cent).
During follow-up, couples reported condomless sex a median of 37 times per year, with MSM couples reporting about 22,000 condomless sex acts and heterosexuals approximately 36,000.
Although 11 HIV-negative partners became HIV-positive (10 MSM; 1 heterosexual; 8 reported condomless sex with other partners), no phylogenetically (molecular characteristics that indicate whether a virus is similar or different from another) linked transmissions occurred over eligible couple-years of follow-up, giving a rate of within-couple HIV transmission of zero.
Researchers said that the confidence limits used in the study suggest that with eligible couple-years accrued so far, appreciable levels of 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 serodifferent couples to practice condomless sex, this study provides informative data (especially for heterosexuals) for couples to base their personal acceptability of risk on," researchers said.
They note that additional longer-term follow-up is necessary to provide a similar level of confidence for the risk from anal sex compared to vaginal sex. The study was published in the journal JAMA.
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