Abstract
Oral HIV pre-exposure prophylaxis (PrEP) is highly effective when taken appropriately at times of HIV risk, termed "prevention-effective adherence". To understand suboptimal adherence, we refined a brief measure for surveys among gay, bisexual and queer men and non-binary (GBQ+) people. We used a mixed-methods design, comprising a national, online cross-sectional survey (June-July 2023) and cognitive interviews (August-October 2023). Logistic regression identified characteristics of PrEP users who reported condomless anal intercourse with casual partners (CLAIC) that was not protected by their own PrEP use because they missed PrEP doses ("PrEP-unprotected CLAIC"). Cognitive interviews investigated whether the prevention-effective adherence measure was comprehensible. Of 2,046 survey respondents, 792 current PrEP users who had CLAIC in the past 6 months were included (Median age = 37, 86.7% gay, 34.5% non-daily-PrEP users). Of PrEP users who reported any CLAIC, 194 (24.5%) reported any PrEP-unprotected CLAIC. They were more likely to: be < 30 years old, be born in Asia vs. Australia, be part-time vs. full-time employed, use non-daily PrEP, have recently initiated PrEP, have experienced side effects from PrEP, and report recent sexualized drug use. They were less likely to find it easy to get PrEP. The 14 interviewees asked about the survey items (Mean age = 33; 50% gay; ) were able to answer the questions and reliably interpret the content. This first national estimate of prevention-effective adherence found that 24.5% of PrEP users who had CLAIC reported any PrEP-unprotected CLAIC. Targeted interventions in subgroups with more frequent PrEP-unprotected episodes must address side effects and other adherence barriers.