Background: ''Be-PrEP-ared'' aims to assess uptake, acceptability and feasibility of daily and event-driven Pre-Exposure Prophylaxis (PrEP) regimens among men who have sex with men (MSM) and transgender women at high risk for HIV. We present findings of regimen choices, sexual behaviour and adherence of the first 12 months of follow-up (FU).
Methods: In this prospective cohort study, participants choose between daily or event-driven Truvada (TDF/FTC). They are allowed to switch, discontinue or restart regimens at three-monthly visits. At each visit, participants receive preventive counselling, fill in a behavioural questionnaire, and provide samples for STI testing. Daily sexual behaviour and PrEP use are self-reported using a web-based diary. We performed an interim analysis on data from baseline (M0) to month 12 (M12).
Results: From 09/2015 - 12/2016, 197 MSM and 3 transgender women were enrolled in the study. Their median age was 38 years (range 22 - 70 yrs).
Initially, 76.5% chose daily and 23.5% event-driven PrEP. Feeling able to anticipate HIV risk was the most frequent reason for preferring event-driven PrEP. During 12 months FU, 28 participants (14%) switched regimen and five discontinued PrEP. Main reasons for switching included changes of life/partner situations, frequency of sexual contacts, simplicity, travel and side effects of Truvada. Adherence, measured as the proportion of participants reporting 100 % high risk sex acts covered by PrEP, was 77.7%, 80.5%, 85.6% and 79.8% at respectively M3, M6, M9 and M12. The reported median number of sexual partners in the past 3 months was 12, 6 and 3 for all, anonymous and occasional partners respectively. These numbers remained steady over the FU period of 12 months and were consistently higher when comparing daily with event-driven users. In total, 54.7% of the participants reported less condom use during receptive anal intercourse with occasional partners at M12 as compared with the baseline. The incidence of bacterial STI was 75% Persons-Years, but no new HIV infections were observed.
Conclusions: Event-driven PrEP was chosen by 23% of the participants and adherence to PrEP was high. Despite high rates of receptive condomless sexual intercourse and STI during FU, no new HIV infections were observed.

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