ART use, viral suppression, and sexual behaviour among HIV-diagnosed MSM in the UK: results from the Antiretrovirals, Sexual Transmission Risk and Attitudes (ASTRA) Study.

Objective: To assess the associations of ART use, viral load (VL) suppression and transmission risk beliefs with sexual behaviour among HIV-diagnosed men who have sex with men (MSM) in the UK. Methods: ASTRA is a multicentre UK study of >3000 HIV outpatients in 2011/12. A self-completed questionnaire defined 'unprotected sex with an HIV-discordant partner' (USD) as anal or vaginal sex without a condom in the past 3 months with a partner of negative or unknown HIV status. Transmission risk belief score (TRBS) was classified as 0-2 [2: agree 'when VL is undetectable, a condom is not needed to prevent HIV transmission'; 1: agree 'undetectable VL makes someone less infectious to a sexual partner' 0: do not agree with either statement]. Associations of USD with TRBS, self-reported ART and VL status, and other factors were assessed using Chi-squared tests and logistic regression. Results: Data are available for 2086 MSM [88% white; mean age: 45 years]. 1767 (84.7%) were on ART; of whom 1470 (83.2%) reported VL≤50 c/mL, 148 (8.4%) reported VL>50 c/mL and 149 (8.4%) did not know VL status. TRBS was 0, 1 and 2 for 48.0%, 47.7% and 4.3% of MSM. Prevalence of USD was 14.8% (n=308) overall; 123 of 308 reported receptive anal sex only. USD prevalence increased with higher TRBS [8.2%, 19.4%, 35.2% for TRBS 0,1,2 respectively; p50 c/mL/unknown (14.7% vs 9.4%; p=0.016). This pattern of association between ART/VL status and USD was similar after adjustment for demographic, lifestyle, and HIV-related factors: compared to MSM on ART with VL50 c/mL/unknown, and 1.25 (0.87, 1.79) for MSM not on ART, global p=0.006. Absence of an HIV-positive stable partner, more recent HIV diagnosis and recreational drug use were also independently associated with USD (all p