Adherence to daily HIV pre-exposure prophylaxis in a large-scale implementation study in New South Wales, Australia

Objectives: To examine patterns of long-term pre-exposure prophylaxis (PrEP) adherence and its association with HIV seroconversion in NSW, Australia.

Design: Population-based HIV PrEP implementation study.

Methods: Expanded PrEP Implementation in Communities in New South Wales was an open-label study of daily oral PrEP which recruited participants from March 2016 to April 2018. Adherence was measured using dispensing records. PrEP discontinuation was defined as an at least 120-day period without PrEP coverage. Long-term adherence patterns were identified using group-based trajectory modelling.

Results: Participants dispensed at least once (n = 9586) were almost all male (98.5%), identified as gay (91.3%), with a median age of 34 years (range: 18-86). Of the 6460 (67.4%) participants who had at least 9 months of follow-up since first dispensing, 1942 (30.1%) discontinued. Among these, 292 (15.0%) restarted later. Four distinct groups were identified ['Steep decline' in adherence (15.8%), 'Steady decline' (11.6%), 'Good adherence' (37.4%), and 'Excellent adherence' (35.2%)]. Older (P < 0.001) and gay-identified (P < 0.001) participants were more likely to have higher adherence, so were those living in postcodes with a higher proportion of gay-identified male residents (P < 0.001). Conversely, those who at baseline reported recent crystal methamphetamine use and had a recent diagnosis of sexually transmitted infection (STI) had lower adherence (P < 0.001). Overall HIV incidence was 0.94 per 1000 person-years (95% confidence interval: 0.49-1.81; n = 9) and was highest in the 'steep decline' group (5.45 per 1000 person-years; P = 0.001).

Conclusion: : About 15% of participants stopped PrEP during study follow-up and were at increased risk of HIV infection. They were more likely to be younger and report a recent STI or methamphetamine use prior to PrEP initiation.