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

•HIV-1 transmission can occur in HIV-1 serodifferent couples who have been prescribed antiretrovirals.•Five seroconversions were noted among 200 HIV serodifferent couples (HIV incidence 2.5%).•Prior mean HIV viral load was higher in HIV transmitters compared to non-transmitters.•Sexually transmitted infection were associated with seroconversion (odds ratio 9.75, 95% confidence interval 1.55–61.2; p=0.023)