PARTER, a new study of more than 750 serodiscordant heterosexual and gay couples who engaged in more than 45,000 condomless sex acts found no cases of linked HIV transmission when the positive partner was on effective antiretroviral therapy (ART), confirming that treatment as prevention works. The results were presented at the 21st Conference on Retroviruses and Opportunistic Infections (CROI 2014) this week in Boston.
AIDSMAPS has published an abstract of the study. here are some of the highlights:
About the study:
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.
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.”
About the participants:
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.
About the Results:
The main news is that in PARTNER so far there have been no transmissions within couples from a partner with an undetectable viral load, in what was estimated as 16,400 occasions of sex in the gay men and 14,000 in the heterosexuals.
Although some of the HIV-negative partners became HIV positive (exactly how many will be revealed in later analyses), genetic testing of the HIV revealed that in all cases the virus came from someone other than the main partner.
Alison Rodger told the conference that if the HIV-positive partners had not been on treatment in this group, 50-100 (median: 86) transmissions would have been expected.
No transmissions is not the same as zero chance of transmission. The researchers calculated the 95% confidence intervals for the results seen. What this means is that they calculated the odds of zero transmissions being the ‘true’ figure and what the maximum possible risk of transmission was, given the results seen.
They established that there was a 95% chance that (in a couple whose sexual activity is average for the group studied) the greatest-possible risk of transmission from a partner was 0.45% per year and from anal sex was 1% a year.
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