- The risk of HIV transmission in gay men serodifferent couples through condomless sex is zero when the HIV-positive partner on antiretroviral therapy (ART) had HIV viral load less than 200 copies per mL.
- No new HIV infections were phylogenetically linked within-couple transmissions during 8 years of follow-up.
- Results support the U=U (undetectable equals untransmittable) campaign and the benefits of early testing and treatment for HIV.
The first phase of the prospective observational PARTNER study reported that the risk of transmission of HIV through condomless sex in the context of virally suppressive ART is zero for heterosexual couples. The aim of PARTNER2 was to provide precise estimates of transmission risk in gay serodifferent partnerships.
PARTNER study recruited heterosexual and gay serodifferent couples (from 75 sites, 14 European countries) from Sept 2010 to May 2014. PARTNER2 extended gay couples enrolment to July 2017. Follow-up ended on April 2018.
Inclusion criteria for couple-years of follow-up (CYFU): condomless sex, no pre/post-exposure prophylaxis in the HIV-negative partner, HIV-positive partner virally suppressed (plasma HIV-1 RNA
Data collection (at baseline and at each visit) included sexual behaviour questionnaires, HIV testing (HIV-negative partner), and HIV-1 viral load testing (HIV-positive partner). If an HIV-negative partner became HIV-positive, phylogenetic analysis was done to compare HIV-1 pol and env sequences to identify linked transmissions.
Primary analysis: incidence rate of HIV transmission calculated as the number of phylogenetically linked HIV infections that occurred during eligible CYFU divided by eligible CYFU.
782 gay couples (median age 38 [interquartile range IQR 31-45] and 40 years [IQR 33-46] for HIV-negative and positive participants, respectively) provided 1.593 eligible CYFU and reported condomless sex for a median of 1 year (IQR 0,4-2,9). Median follow-up: 2 years (IQR 1,1-3,5).
Total condomless anal sex acts during eligible CYFU: 76.088.
37% (288/777) of HIV-negative men reported condomless sex with other partners.
15 of the initially HIV-negative partners became HIV-1 positive. There were no within-couple phylogenetically linked transmissions, thus the estimated rate for HIV transmission was zero (upper 95% CI 0,23 per 100 CYFU).
Results support the message of the U=U campaign: risk of HIV transmission in the context of virally suppressive ART is zero. This campaign can be applied when HIV-positive people have access to testing, effective treatment, viral load monitoring and full support to maintain high levels of adherence.
Limitations: it was not possible to determine the risk of HIV transmission in very new partnerships; most HIV-positive partners had been on ART for several years.