Zero HIV Transmissions in Mixed-Status Couples Having Condomless Sex
As reported today at the 21st Conference on Retroviruses and Opportunistic Infections, the multinational PARTNER study found zero HIV transmissions from condomless sex within mixed-HIV-status couples when the HIV-positive partner had his or her viral load suppressed below 200 copies/mL.
Alison Rodger of University College London presented interim data from the study, which involved “serodifferent” couples who reported having condomless sex and not using PrEP or PEP (post-exposure prophylaxis), and in which the HIV-positive partner was on suppressive antiretroviral therapy (ART).
“I think we all acknowledge it’s critical to understand the absolute risk of sexual transmission of HIV through condomless sex for a person on ART with an undetectable viral load,” Rodger stated.
Every six months, PARTNER study participants completed a confidential sexual behavior questionnaire, and HIV-negative partners were tested for HIV infection. “Couple-years” of follow-up—that is, the number of years each couple was followed during the study—were included in this interim analysis only if the pair reported continued condomless sex without using PrEP or PEP, and if the HIV-positive partner’s latest viral load was below 200 copies/mL.
Although participants received counseling around condom use, only data from couples who reported having sex without condoms were included in the analysis.
In total, 767 couples contributed 894 eligible couple-years of follow-up (CYFU for short). New HIV infections were phylogenetically linked: Researchers analyzed samples of HIV from the newly infected partner and the HIV-positive partner to determine whether the transmission occurred within the couple or originated with an outside partner.
The analysis included 282 gay male couples and 445 heterosexual couples. The estimated number of penetrative sex acts (with or without ejaculation) was 16,416 in gay male couples, 13,728 in heterosexual couples with an HIV-positive male partner, and 14,295 in heterosexual couples with an HIV-positive female partner, for a grand total of approximately 44,439 sex acts. During the study, couples had condomless sex a median of 45 times per year.
“In the absence of ART, we would expect to see a significant number of transmissions,” Rodger noted. “In fact, for HIV-negative MSM [men who have sex with men], based on the number and type of sex acts, we would have expected approximately 86 transmissions in the absence of ART.” The total number of sex acts across the two groups would have been expected to result in 50 to 100 HIV transmissions in the absence of ART, added Jens Lundgren of the University of Copenhagen in a press conference.
HIV transmissions did occur in follow-up—but only from outside partners, Rodger explained. None were phylogenetically linked to the original HIV-positive individual in any couple. “Overall, we had no linked transmissions during eligible follow-up, giving a transmission rate of zero.”
This important finding speaks to the added preventive benefit of effective HIV treatment, and fills a gap in the research literature regarding the efficacy of “treatment as prevention” in gay male couples.
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However, the longer-term transmission risk linked with suppressive ART may not be zero, Rodger and Lundgren both emphasized. Although no within-couple transmissions occurred over the study period in this particular sample of mixed-HIV-status couples, the study team’s statistical analysis estimates that overall ten-year risk is 4% for any of the reported penetrative sex acts, close to 10% for anal sex, and 32% for receptive anal sex with ejaculation.
Zero transmission risk “is our best guess,” explained Rodger, but more data are needed—particularly for couples having anal sex with ejaculation—to strengthen estimates of transmission risk in the setting of viral suppression.
To this end, the PARTNER2 study aims to enroll and follow 450 gay male couples through 2017. The goal of this further study, Rodger explained, is “to provide more precise estimates for transmission risk, to inform policy, [and] also to inform individual choice on whether to use condoms or not.”
“It really is up to people themselves to judge if anything they do in life is ‘safe’ or ‘not safe,’” Lundgren stressed in the March 4 press conference. That said, these interim results have implications for legal issues around HIV, and for avoiding unnecessary use of post-exposure prophylaxis: If the HIV-positive partner has a fully suppressed viral load, Lundgren observed, “there is no reasonable legal action you could take against people who aren’t using condoms, and there’s really not a major concern if the condom breaks—and there’s certainly no indication for PEP.”
There’s more from CROI 2014—see BETA’s complete conference coverage.
Reilly O’Neal is a freelance writer and former editor of BETA.
153LB: HIV Transmission Risk Through Condomless Sex If HIV+ Partner On Suppressive ART: PARTNER Study
Alison Rodger, Tina Bruun, Valentina Cambiano, Pietro Vernazza, Vicente Estrada, Jan Van Lunzen, Simon Collins, Anna Maria Geretti, Andrew Phillips, Jens Lundgren, for the PARTNER Study Group
Background: The absolute risk of sexual HIV transmission on stable ART (HIV RNA viral load (VL) <200 c/mL) from condomless sex is unknown. Current limited data are largely focusing on vaginal sex.
Methodology: The international, observational multi-centre PARTNER study prospectively follows serodifferent couples (heterosexual (HT) and MSM) who had condomless penetrative anal or vaginal sex in the month prior to study entry, and where the HIV+ve partner is on ART. Every 6 months, each partner completes a sexual behaviour questionnaire and the negative partner tests for HIV. Eligibility of follow-up time in this transmission rate analysis required: continued condomless sex; not using PEP or PrEP; and latest VL <200 c/mL. For new diagnoses, phylogenetic analysis compared HIV-1 pol and env sequences by couple, after samples were anonymised. This planned analysis reports the rate of occurrence of linked transmissions.
Results: By 1st November 2013, 1110 couples were enrolled. Of 1151 couple-years of follow-up (CYFU), 894 were eligible (586 in HT and 308 in MSM). At baseline, the median duration on ART was 4.9 years (IQR: 1.9-11.4) and couples reported having condomless sex for a median 2 years (IQR: 0.5-6.3). Condomless sex with a different partner outside the partnership during follow-up was reported by 27% MSM and 2% HT HIV-negative partners. During follow-up, couples had condomless sex a median of 45 times/ year (IQR: 16-90). Although some negative partners became HIV positive during FU, no phylogenetically linked transmissions occurred, giving a rate of within-couple HIV transmission during eligible couple-years of zero (95% CI: 0-0.40/100 CYFU)(Table). The upper limit of the 95% CI for the rate of transmission was 0.96/100 CYFU for condomless anal sex (HT and MSM) and 1.97/100 CYFU for condomless receptive anal sex with or without ejaculation (MSM).
Conclusions: The overall risk of HIV transmission (in the context of previous sex without transmission) through condomless anal or vaginal sex from HIV positive people on ART with plasma VL < 200 copies/mL is extremely low, but uncertainty over the risk remains, particularly over receptive anal sex. Additional follow-up in MSM is essential to provide more precise estimates for transmission risk given the current assumptions of safety in some communities.