The second large study to look at whether people with HIV become non-infectious if they are on antiretroviral therapy (ART) has found no cases where someone with a viral load under 200 copies/ml transmitted HIV, either by anal or vaginal sex.
Published: March 4, 2014
Statistical analysis shows that the maximum likely chance of transmission via anal sex from someone on successful HIV treatment was 1% a year for any anal sex and 4% for anal sex with ejaculation where the HIV-negative partner was receptive; but the true likelihood is probably much nearer to zero than this.
When asked what the study tells us about the chance of someone with an undetectable viral load transmitting HIV, presenter Alison Rodger said: "Our best estimate is it’s zero."
The previous study, HPTN 052, established in 2011 that the efficacy of antiretroviral therapy in the HIV-positive partner was at least 96% in heterosexual couples, but had too few gay couples in it to establish if the same applied to them (or rather to anal sex).
The PARTNER study was designed to remedy this gap in knowledge. It has so far recruited 1110 couples where the partners have differing HIV status – and nearly 40% of them are gay couples.
In order to be in the study, couples have to be having sex without condoms at least some of the time. The HIV-negative partner cannot be using post-exposure or pre-exposure prophylaxis (PEP or PrEP) and the HIV-positive partner has to be on ART, with the most recent viral load below 200 copies/ml. This is different from HPTN052, which measured the efficacy of the HIV positive partner starting therapy (versus partners who did not).
In total, 767 couples took part in this two-year interim analysis and there were a total of 894 couple-years of follow-up. Among the heterosexual couples, HIV serostatus was split evenly – in half the couples the man had HIV and in the other half, the woman.
Some couples were excluded from this analysis. In most cases, this was because they did not attend follow-up appointments but in 16% of cases it was because the HIV-positive partner developed a viral load above 200 copies/ml, and in 3% of cases because the HIV-negative partner took PEP or PrEP.
There were significant differences between the gay and heterosexual couples. At baseline, gay couples had been having condomless sex for a shorter period on average: 1.5 years versus 2.5 for heterosexual men and 3.5 for women.
During the follow-up period, all the heterosexual HIV-negative partners reported condomless vaginal sex, 72% with ejaculation; 70% of the gay HIV-negative partners reported receptive anal sex, 40% with ejaculation, while 30% reported only being the insertive partner. A significant proportion of the heterosexual couples reported anal sex (to be reported later).
Condomless sex outside the relationship was much more common in the gay men – a third of the HIV-negative partners reported this, versus 3-4% of heterosexuals. No doubt because of this, sexually transmitted infections (STIs) were much more common in the gay couples, with16% of gay men developing an STI (mainly gonorrhoea or syphilis) during the follow-up period versus 5% of the heterosexuals.
At the start of the study, the HIV-positive partner had been on ART for five years in the gay couples and for 7-10 years in the heterosexuals; the proportion reporting an undetectable viral load was 94% in the gay men and 85-86% in the heterosexuals.
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