Retention of men who have sex with men in a pre-exposure prophylaxis programme: survival analysis from a crossover study

Background Adherence to monitoring and prescription of pre-exposure prophylaxis (PrEP) is important in effectively preventing HIV infection. We aimed to establish the retention rate of men who have sex with men (MSM) who enrolled in a PrEP implementation study in Hong Kong, China. Methods Our study was a survival analysis of a crossover study. A research clinic was set up in the teaching hospital of the university to recruit participants through community-based organisations or by self-referral. Participants were randomly assigned by block randomisation with a block size of four to two groups during the study period (32 weeks split into two 16-week phases); in the first group, participants were asked to take PrEP every day for the first 16 weeks then on demand for the remaining 16 weeks, and in the second group, participants took PrEP on demand for the first 16 weeks then ever day for the remaining 16 weeks. Eligible participants were adult HIV-negative MSM with a history of high HIV-risk behaviours or sexually transmitted infections in the preceding 6 months and an inclination to practice condomless sex in the coming 6 months. The exclusion criteria were hepatitis B virus infection, creatinine clearance lower than 60 mL per min, with or without mental illnesses. We assessed behavioural factors associated with retention by bivariate analysis. We used cox regression to characterise participants who had dropped out of the study. The study was approved by the Joint Chinese University of Hong Kong-New Territories East Cluster Clinical Research Ethics Committee (CREC 2016.719). The trial is registered with the Centre for Clinical Research and Biostatistics, The Chinese University of Hong Kong, Hong Kong, China (trial number CUHK_CCRB00606). Findings Between Aug 25, 2018, and Mar 23, 2019, we recruited 120 MSM. Of the 120 MSM recruited, one (<1%) tested positive for HIV at baseline and was therefore excluded and referred to HIV services. Of the remaining 119 participants, with a median age of 30 years (interquartile range 26–38 years), 59 (50%) were assigned to the daily-PrEP-first group and 60 (50%) were assigned to the on-demand-PrEP-first group. Some 103 (87%) MSM attended all scheduled visits. Study group was not associated with retention status (p=0·97) with 51 (86%) of 59 MSM completing 32 weeks follow-up in the daily-PrEP-first group and 52 (87%) of 60 MSM completing follow-up in the on-demand-PrEP-first group. Participants who discussed PrEP use with their boyfriends were more likely to drop out (p=0·030). After excluding one participant who defaulted after the first visit, results from cox regression showed that MSM who were on PrEP before joining this study had a dropout hazard of 0·256 and those who had HIV-positive sex partners had a dropout hazard of 9·513. The hazard increased by 10% for each year of age. Discordant results were found in the effect of sexual role. On a scale of 1 to 10 ranking inclination to have insertive condomless anal sex, the hazard decreased by 20% for each increasing point, whereas receptive roles increased by 30%. Interpretation The retention was high in a trial setting. Defaulters who had receptive anal sex or HIV-positive sex partners might have continued HIV risk, therefore other prevention measures should be made available if PrEP was not sought elsewhere. The role of intimate or sex partners in retention in PrEP programmes should be explored. Funding AIDS Trust Fund (MSS 292 R).