HIV Transmission Risk Among Serodiscordant Couples: PARTNER Study Findings

The HPTN 052 study (NEJM JW Infect Dis Sep 2011 and N Engl J Med 2011; 365:493) showed that treatment of HIV infection decreases the risk for sexual transmission. However, most of the available data so far comes from heterosexual couples or when condoms are also being used. To understand the risks of anal sex and of vaginal sex without condoms in which the HIV-infected partner is virally suppressed on antiretroviral therapy (ART), European investigators conducted an observational, multicenter study.

A total of 1166 couples were enrolled, of which 888 couples contributed 1238 couple-years of follow-up: 269 heterosexual in which the male partner was infected, 279 heterosexual in which the female partner was infected, and 340 men who have sex with men (MSM). Adherence to ART was >93%, and virtually all HIV-infected participants had a viral load <50 copies/mL. Median number of condomless sex acts within the partnership was 42 per year for MSM and 35 and 36, respectively, for HIV-negative heterosexual men and women; 33% of HIV-negative MSM and 4% of HIV-negative heterosexuals reporting condomless sex with other partners. During a median follow-up of 1.3 years per couple, 11 HIV-negative individuals became HIV-infected — 10 MSM and 1 heterosexual, of whom 8 reported sex with other partners — but no phylogenetically linked transmissions occurred. The upper 95% confidence limit for within-couple transmission was 0.30 per 100 couple-years of follow-up.