Impact of early antiretroviral treatment on sexual behaviour in the INSIGHT Strategic Timing of Anti-Retroviral Treatment (START) Trial: A randomised comparison

BACKGROUND: Antiretroviral treatment (ART) reduces HIV infectiousness, but the effect of early ART on sexual behaviour is unclear.

METHODS: We assessed, within the START randomised trial that enrolled HIV-positive adults with CD4>500/mm, the effect of early (immediate) versus deferred ART on: (i) condomless sex with HIV-serodifferent partners (CLS-D); (ii) all condomless sex (CLS); (iii) HIV transmission-risk-sex (CLS-D-HIV-risk, defined as CLS-D and: not on ART or started ART < 6 months ago or viral load(VL)>200c/mL or no VL in past 6 months), during two year follow-up. Month-12 CLS-D (2010-2014) was the primary outcome.

RESULTS: Among 2562 MSM, there was no difference between immediate and deferred arms in CLS-D at month 12 [12.6% versus 13.1%; difference (95% CI): -0.4% (-3.1%, 2.2%), p = 0.75] or month 24, or in CLS. Among 2010 heterosexual men and women, CLS-D at month 12 tended to be higher in the immediate versus deferred arm [10.8% versus 8.3%; difference:2.5% (-0.1%, 5.2%), p = 0.062]; the difference was greater at month 24 [9.3% versus 5.6%; difference:3.7%(1.0%, 6.4%), p = 0.007], at which time CLS was higher in the immediate arm [20.7% versus 15.7%, p = 0.013]. CLS-D-HIV-risk at month 12 was substantially lower in the immediate versus deferred arm for MSM [0.2% versus 11.0%; difference: -10.7% (-12.5%, -8.9%), p < 0.001] and heterosexuals [0.6% versus 7.7%; difference: -7.0% (-8.8%, -5.3%), p < 0.001], due to viral suppression on ART.

CONCLUSIONS: A strategy of early ART had no effect on condomless sex with HIV-serodifferent partners among MSM, but resulted in modestly higher prevalence among heterosexuals. However, among MSM and heterosexuals, early ART resulted in a substantial reduction in HIV-transmission-risk-sex, to a very low absolute level.