HIV-1 heterosexual transmission and association with sexually transmitted infections in the era of treatment as prevention.

OBJECTIVES: HIV-1 heterosexual transmission among individuals on antiretroviral treatment (ART) with undetectable viremia is extremely rare. The aim of this study was to evaluate the risk of sexual HIV-1 transmission and other sexually transmitted infections (STIs) in HIV-1 serodifferent couples while the index partner is on ART. METHODS: HIV transmission was evaluated in 200 HIV-1 heterosexual serodifferent couples in a stable relationship (≥3 months). All HIV-positive individuals had been on ART for ≥3 months and had been followed up for a median preceding time of 4.5 years (range 0.3-16 years) at the HIV couples clinic at Hospital Nossa Senhora da Conceição in Porto Alegre, Brazil. Following written informed consent, participants responded to demographic/behavioral questionnaires. Quantitative PCR for HIV RNA, T-cell subsets, and STI testing (syphilis, herpes, human papillomavirus, gonorrhea, and bacterial vaginosis) were performed. Self-collected vaginal swabs were obtained for quantitative HIV genital viral load testing. RESULTS: Among 200 couples, 70% of index partners were female. Five seroconversions were observed; the HIV infection incidence was 2.5% (95% confidence interval 0.8% to 5.7%). Mean plasma viral load results were higher in HIV transmitters compared to non-transmitters (p=0.02). The presence of STIs was significantly greater in couples who seroconverted (60.0% vs. 13.3%; odds ratio 9.75, 95% confidence interval 1.55-61.2; p=0.023). The duration of undetectable HIV viremia and presence of STIs were associated with HIV transmission. CONCLUSIONS: Undetectable viremia was the main factor associated with non-transmissibility of HIV in this setting.