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  International AIDS Conference
Durban, South Africa
July 18-22 2016
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No Transmissions in Couples With HIV+ Partner Undetectable on ART
  21st International AIDS Conference (AIDS 2016), July 18-22, 2016, Durban, South Africa
Mark Mascolini
HIV-positive people with a viral load below 200 copies/mL while taking antiretroviral therapy (ART) did not transmit HIV to steady sex partners during condomless sex through 1.3 years of follow-up in the European PARTNER Study [1]. Eleven HIV-negative partners, including 10 men who have sex with men (MSM), did become infected during follow-up, but phylogenetic analysis did not link the infecting virus to their on-treatment partner. However, the short follow-up so far and the upper 95% confidence limits for transmission hint that suppressive ART without condoms may not be a foolproof prevention strategy.
The international HPTN 052 trial found that starting ART immediately--at a high CD4 count--lowered chances of HIV transmission to steady sex partners 96% compared with delayed ART [2]. PARTNER investigators planned their study to determine HIV transmission rates in couples reporting condom-free sex when the HIV-positive partner had a viral load below 200 copies/mL while taking ART.
The PARTNER team recruited HIV-discordant heterosexual or gay couples from 75 sites in 14 European countries. The HIV-positive partner was taking ART and the couples reported anal or vaginal sex without a condom in the past month and expected to continue having sex in coming months. Every 6 to 12 months, researchers measured HIV RNA in positive partners, while testing negative partners for HIV infection. If the negative partner became positive, the investigators sequenced the infecting virus and the positive partner's virus to see if they were genetically related. Couples were eligible for the HIV transmission analysis if (1) they had condomless sex in the period between HIV tests, (2) partners did not use PEP or PrEP, (3) the latest viral load of the positive partner lay below 200 copies/mL, and (4) follow-up occurred before May 31, 2014.
The transmission analysis focused on 888 couples, 548 of them heterosexual and 340 MSM. Among the 548 heterosexual couples, the woman was the positive partner in 279 couples and the man in 269 couples. During 94% of follow-up time, viral loads in the positive partner lay below 50 copies; during the remaining 6% of follow-up time, viral loads lay between 50 and 200 copies. Median age stood between 40.1 and 44.9 in heterosexual men, MSM, and women. Self-reported antiretroviral adherence was 93% in heterosexual men, 97% in MSM, and 94% in women. During eligible follow-up time, MSM reported a median of 42 condomless sex acts per year with their study partner, heterosexual men 35, and women 36. Meanwhile, 4% of heterosexual men and women and 33% of MSM reported condomless sex outside their main partnership.
During a median follow-up of 1.3 years, 11 of 888 (1.2%) initially HIV-negative partners (10 MSM and 1 heterosexual) became infected. None of these 11 infections could be linked to the HIV-positive partner. Eight of 11 newly infected people reported recent condomless sex with someone other than their study partner. Thus estimated transmission during condomless sex at a time when the initially positive partner's viral load lay below 200 copies was 0, and the upper 95% confidence limit for transmission was 0.30 per 100 couple-years. For heterosexuals the upper 95% confidence limit for all sex was 0.97 per 100 couple-years with a male-positive partner and 0.88 with a female-positive partner. For MSM the upper 95% confidence limit for all sex was 0.84 per 100 couple-years. The highest 95% confidence limit was 2.23 per 100 couple-years for receptive anal sex with ejaculation in a combined heterosexual-MSM analysis.
The PARTNER team cautioned that these 95% confidence limits "suggest that with eligible couple-years accrued so far, appreciable levels of risk cannot be excluded" [3]. But the 0 overall linked transmissions recorded so far during frequent condomless sex underline the value of ART alone as a prevention strategy: Without ART, more than 100 HIV transmissions would be expected in MSM in this study, given the frequency and type of sex acts they reported.
In an editorial accompanying the published PARTNER study [4], UCLA's Eric Daar and Katya Corado spelled out other caveats in interpreting these findings: (1) Couples in stable relationships, like the PARTNER couples, may run a lower risk of HIV transmission than casual sex partners. (2) Positive partners had been taking ART for a median of 7.5 years, which may influence chances of transmission. (3) Self-reported adherence was high in positive PARTNER participants. (4) Although PARTNER couples reported ongoing condomless sex, negative partners received counseling on transmission risk and were strongly encouraged to use condoms. (5) Couples were in care and were probably being tested and treated for sexually transmitted infections (STIs) that could boost HIV transmission risk.
Daar and Corado suggested that clinicians "emphasize to patients that the use of condoms is an important measure to prevent transmission of STIs and advise them that having a virologically suppressed partner does not protect the HIV-uninfected person from acquiring HIV from other individuals outside the relationship" [4].
1. Rodger A. Association between sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy: the PARTNER study. 21st International AIDS Conference (AIDS 2016). July 18-22, 2016. Durban, South Africa. Abstract TUAC0206.
2. Cohen MS, Chen YQ, Marybeth McCauley M, et al. Prevention of HIV-1 infection with early antiretroviral therapy. N Engl J Med. 2011;365:493-505. http://www.nejm.org/doi/full/10.1056/NEJMoa1105243
3. Rodger AJ, Cambiano V, Bruun T, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy. JAMA. 2016;316:171-181. http://jama.jamanetwork.com/article.aspx?articleid=2533066
4. Daar ES, Corado K. Condomless sex with virologically suppressed HIV-infected individuals: how safe is it? JAMA. 2016;316:149-151. http://jama.jamanetwork.com/article.aspx?articleid=2533043