Undetectable HIV status is untransmittable in condomless sex, study confirms
The risk of HIV transmission is “effectively zero” among gay couples who have condomless anal sex when the HIV viral load is suppressed, according to a new study.
“Our findings support the message of the U=U (undetectable equals untransmittable) campaign, and the benefits of early testing and treatment for HIV,” researchers said.
Of the 972 gay couple enrolled between 15 September 2010 and 31 July 2017, 782 provided 1,593 eligible couple-years of follow-up (median follow-up, 2.0 years; interquartile range [IQR], 1.1–3.5). At baseline, HIV-positive partners had a median age of 40 years (IQR, 33–46 years) and couples reported condomless sex for a median of 1.0 year (IQR, 0.4–2.9 years).
Condomless anal sex was reported 76,088 times during eligible couple-years of follow-up, while 288 (37 percent) of 777 HIV-negative men reported condomless sex with other partners. [Lancet 2019;doi:10.1016/S0140-6736(19)30418-0]
In all, 15 new HIV infections emerged during eligible couple-years of follow-up. However, none of these were phylogenetically linked to within-couple transmissions. Thus, the rate of HIV transmission was zero (upper 95 percent CI, 0.23 per 100 couple-years of follow-up).
“Our findings provide conclusive evidence that the risk of HIV transmission through anal sex when HIV viral load is suppressed is effectively zero,” researchers claimed.
Unlike other studies on HIV transmission, this research only recruited couples who had chosen not to use condoms and with no use of pre- (PrEP) or postexposure prophylaxis (PEP) by the HIV-negative partner. Results showed no linked transmissions across all types of sexual behaviour and during periods when the HIV-positive or -negative partner reported sexually transmitted infection (STI).
Similarly, the Opposites Attract Study found no HIV transmissions during periods in which STIs were reported (21 couple-years of follow-up). [Lancet HIV 2018;5:e438-e447]
The current prospective, observational study was conducted at 75 sites in 14 European countries. Data from sexual behaviour questionnaires, HIV testing (HIV-negative partner) and HIV-1 viral load testing (HIV-positive partner) were collected at study visits.
The investigators performed anonymized phylogenetic analysis if seroconversion occurred in the HIV-negative partner to compare HIV-1 pol and env sequences in both partners to identify linked transmissions. Couple-years of follow-up were eligible for inclusion if condomless sex was reported, use of PrEP or PEP was not reported by the HIV-negative partner, and the HIV-positive partner was virally suppressed (plasma HIV-1 RNA <200 copies per mL) at the most recent visit (within the past year).
HIV transmission rate was calculated as the number of phylogenetically linked HIV infections that occurred during eligible couple-years of follow-up divided by eligible couple-years of follow-up. Exact Poisson methods were used to estimate two-sided 95 percent CIs for the incidence rate of transmission.
“One limitation of the study was that most couples had been having sex without condoms for more than 6 months before study entry,” the investigators said. “Although there is little evidence that some individuals might be more susceptible to early acquisition of HIV infection, we were unable to determine risk of HIV transmission in very new partnerships.”