Heterosexual HIV-1 transmission after initiation of antiretroviral therapy: a prospective cohort analysis

Background High plasma HIV-1 RNA concentrations are associated with increased risk of HIV-1 transmission. Initiation of antiretroviral therapy (ART) reduces plasma HIV-1 concentrations. We aimed to assess the effect of ART use by patients infected with HIV-1 on risk of transmission to their uninfected partners. Methods Participants in our prospective cohort analysis were from a randomised placebo-controlled trial that enrolled heterosexual African adults who were seropositive for both HIV-1 and herpes simplex virus type 2, and their HIV-1 seronegative partners. At enrolment, HIV-1 infected participants had CD4 counts of 250 cells per mu L or greater and did not meet national guidelines for ART initiation; during 24 months of follow-up, CD4 counts were measured every 6 months and ART was initiated in accordance with national guidelines. Uninfected partners were tested for HIV-1 every 3 months. The primary outcome was genetically-linked HIV-1 transmission within the study partnership. We assessed rates of HIV-1 transmission by ART status of infected participants. Findings 3381 couples were eligible for analysis. 349 (10%) participants with HIV-1 initiated ART during the study, at a median CD4 cell count of 198 (IQR 161-265) cells per mu L. Only one of 103 genetically-linked HIV-1 transmissions was from an infected participant who had started ART, corresponding to transmission rates of 0.37 (95% CI 0.09-2.04) per 100 person-years in those who had initiated treatment and 2.24 (1.84-2.72) per 100 person-years in those who had not-a 92% reduction (adjusted incidence rate ratio 0.08,95% CI 0.00-0.57, p=0.004). In participants not on ART, the highest HIV-1 transmission rate (8.79 per 100 person-years) was from those with CD4 cell counts lower than 200 cells per pL. In couples in whom the untreated HIV-1 infected partner had a CD4 cell count greater than 200 cells per pL, 66 (70%) of 94 transmissions occurred when plasma HIV-1 concentrations exceeded 50 000 copies per mL. Interpretation Low CD4 cell counts and high plasma HIV-1 concentrations might guide use of ART to achieve an HIV-1 prevention benefit. Provision of ART to HIV-1 infected patients could be an effective strategy to achieve population-level reductions in HIV-1 transmission.