Studying the Digital Intervention Engagement-Mediated Relationship Between Intrapersonal Measures and Pre-Exposure Prophylaxis Adherence in Sexual and Gender Minority Youth: Secondary Analysis of a Randomized Controlled Trial

Background: Improvingadherence topre-exposure prophylaxis (PrEP)via digital health interventions (DHIs) for young sexual and gender minority men who have sex with men (YSGMMSM) is promising for reducing the HIV burden. Measuring and achieving effective engagement (sufficient to solicit PrEP adherence) in YSGMMSM is challenging. Objective: This study is a secondary analysis of the primary efficacy randomized controlled trial (RCT) of Prepared, Protected, Empowered (P3), a digital PrEP adherence intervention that used causal mediation to quantify whether and to what extent intrapersonal behavioral, mental health, and sociodemographic measures were related to effective engagement for PrEP adherence inYSGMMSM. Methods: In May 2019, 264 YSGMMSM were recruited for the primary RCT via social media, community sites, and clinics from 9 study sites across the United States. For this secondary analysis, 140 participants were eligible (retained at follow-up, received DHI condition in primary RCT, and completed trial data). Participants earned US currency for daily use of P3 and lost US currency for nonuse. Dollars accrued at the 3-month follow-up were used to measure engagement. PrEP nonadherence was defined as blood serum concentrations of tenofovir-diphosphate and emtricitabine-triphosphate that correlated with <= 4 doses weekly at the 3-month follow-up. Logistic regression was used to estimate the total effect of baseline intrapersonal measures on PrEP nonadherence, represented as odds ratios (ORs) with a null value of 1. The total OR for each intrapersonal measure was decomposed into direct and indirect effects. Results: For every US $1 earned above the mean (US $96, SD US $35.1), participants had 2% (OR 0.98, 95% CI 0.97-0.99) lower odds of PrEP nonadherence. Frequently using phone apps to track health information was associated with a 71% (OR 0.29, 95% CI 0.06-0.96) lower odds of PrEP nonadherence. This was overwhelmingly a direct effect, not mediated by engagement, with a percentage mediated (PM) of 1%. Non-Hispanic White participants had 83% lower odds of PrEP nonadherence (OR 0.17, 95% CI 0.05-0.48) and had a direct effect (PM=4%). Participants with depressive symptoms and anxiety symptoms had 3.4 (OR 3.42, 95% CI 0.95-12) and 3.5 (OR 3.51, 95% CI 1.06-11.55) times higher odds of PrEP nonadherence, respectively. Anxious symptoms largely operated through P3 engagement (PM=51%). Conclusions: P3 engagement (dollars accrued) was strongly related to lower odds of PrEP nonadherence. Intrapersonal measures operating through P3 engagement (indirect effect, eg, anxious symptoms) suggest possible pathways to improve PrEP adherence