BACKGROUND: Digital health interventions (DHIs) for Pre-Exposure Prophylaxis (PrEP) in young sexual and gender minority men who have sex with men (YSGMMSM) show promise for reducing HIV burden. Effectively engaging (engagement sufficient to solicit PrEP adherence) YSGMMSM is an ongoing challenge.
METHODS: This secondary analysis of the P3 (Prepared, Protected, emPowered: a digital PrEP adherence intervention) randomized controlled trial (RCT) utilized causal mediation to quantify whether and to what extent baseline survey measures of phone and phone app usage, mental health, and sociodemographics were related to effective engagement for PrEP adherence in YSGMMSM. Of 246 YSGMMSM participants aged 16-24 in the primary RCT, 140 participants were eligible for the present analysis (retained at folloâ??w-up, received DHI condition, complete trial data). Participants earned and lost US currency for daily usage/non-usage of P3; dollars accrued by 3 months was used to measure engagement. PrEP non-adherence was measured via blood serum levels consistent with textless4 doses weekly at 3-month follow-up. Logistic regression was used in a causal mediation approach to estimate the total effects of baseline survey measures, represented as non-adherence odds ratios (NAR), and direct and indirect effects mediated by engagement.
RESULTS: Engagement was strongly related to the outcome: for every $1 earned above the mean ($96), participants had 1.6% (NAR=0.984, 95% CI=0.97,0.99) lower odds of PrEP non-adherence. Frequently using phone apps to track health information was associated with a 71% (NAR=0.29, 95% CI=0.06,0.96) lower odds of PrEP non-adherence. This was overwhelmingly a direct effect, not mediated by engagement, with a percent mediated (PM) of 1%. Participants with depressive symptoms and anxious symptoms had 3.4 (NAR=3.42, CI=0.95,12.00) and 3.5 (NAR=3.51, CI=1.06,11.55) higher odds of non-adherence to PrEP at 3 months, respectively. Anxious symptoms largely operated through P3 engagement (PM=51%).
CONCLUSIONS: P3 engagement was strongly related to lower odds of PrEP non-adherence. Several measures were related to effective engagement which suggests that PrEP adherence DHIs for YSGMMSM should tailor intervention content to emphasize engagement facilitators and abate engagement barriers. Evaluating effective engagement in DHIs with causal mediation approaches provides a clarifying and mechanistic view of how DHIs impact health behavior.