HIV-positive people with a viral load below 200 copies/mL while on antiretroviral therapy (ART) did not transmit HIV to steady sex partners during more than one year of condomless sex in the European PARTNER Study. 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. Confidence limits and short follow-up so far suggest, however, that "appreciable levels of risk cannot be excluded."
HPTN 052 and other studies showed that HIV-positive people with ART-suppressed viremia have an exceedingly low risk of transmitting HIV to their sex partners. To determine transmission risk from virally suppressed HIV-positive European partners having vaginal or anal sex, the PARTNER Study Group conducted this prospective observational analysis.
From September 2010 to May 2014, researchers recruited HIV-discordant partners (one HIV-positive, one negative) at 75 clinical sites in 14 European countries. To be included in the transmission analysis, partners had to report (1) condomless vaginal or anal sex in the months before enrollment, (2) continued condomless sex during the study period, (3) no use of pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP) and (4) latest viral load in initially positive partner below 200 copies/mL on ART.
Negative partners were tested for HIV infection every 6 to 12 months, while positive partners had their viral loads tested at the same intervals. If a negative partner acquired HIV infection, viral pol and env sequences from both partners were tested to determine whether the partners' HIV was genetically related.
The transmission analysis involved 888 couples, including 548 heterosexual couples and 340 MSM couples. Among heterosexual couples, 279 (51%) had an HIV-positive female partner and 269 a positive male partner. Median ages of MSM and heterosexual men and women ranged from 40.1 to 44.9 years. About 80% of participants were white. Median follow-up measured 1.3 years per couple and overall follow-up totaled 1238 couple-years. Among HIV-negative partners, MSM reported a median of 42 condomless sex acts per year, heterosexual men reported 35 and heterosexual women reported 36.
During follow-up, 11 initially negative partners acquired HIV infection, including 10 MSM and one heterosexual. Eight of these 11 people reported recent condomless sex with someone other than their regular partner. HIV sequence analysis found no evidence indicating that newly infected partners acquired HIV from their study partner.
HIV transmission rate from positive to initially negative partners was 0 for MSM and for heterosexual men and women. The rate was 0 for vaginal sex, insertive anal sex and receptive anal sex with ejaculation. Upper 95% confidence limits for certain subgroups were higher than the overall upper 95% confidence limit of 0.30 per 100 couple-years for any sex, for example, receptive anal sex with ejaculation in MSM (2.70) or heterosexual women (12.71) and insertive anal sex in heterosexual men (7.85).
Although the transmission rate for vaginal or anal sex was 0, the PARTNERS investigators cautioned that "95% confidence limits suggest that with eligible couple-years accrued so far, appreciable levels of risk cannot be excluded." The researchers stressed that their results "cannot directly provide an answer to the question of whether it is safe for serodifferent couples to practice condomless sex."
Still, despite the median follow-up of 1.3 years per couple, the authors noted that their analysis "contains more than 3 times the couple-years of follow-up for condomless sex than all the other previous studies combined, including more than 500 couple-years of follow-up of condomless anal sex."