User engagement in the tuberculosis treatment support tools intervention and its impact on treatment outcomes: A secondary analysis of a pragmatic trial

Digital adherence technologies (DATs) may improve health behaviors only when users engage, but links between engagement, user factors, and outcomes are unclear. TB Treatment Support Tools (TB-TST) is a DAT with a smartphone app connecting patients to treatment supporters and weekly drug metabolite testing. We evaluated TB-TST app engagement in a pragmatic randomized controlled trial and identified factors associated with adherence and treatment outcomes. Engagement was measured from app interactions by 277 participants over 180-days of TB treatment. Adherence was assessed via daily self-reports and weekly metabolite-test photo submissions. Participants could also message treatment supporters, report side effects, or request help. We modeled time to non-adherence (28 consecutive days without reporting) using survival analysis. Logistic regression tested associations of adherence and engagement with treatment outcomes. A latent engagement score was derived using confirmatory factor analysis (CFA) from medication reports, photo submissions, side-effect reports, messaging, and overall adherence. Participants submitted 24,902 medication reports, 2,926 messages, 2,465 photos, 1235 side effect reports, and 128 help requests. Adherence declined over time (78% at 60 days; 50% at 180 days). Non-adherence was more common among males, participants living at or below the poverty line, those without stable employment, and those treated at certain hospitals. Non-adherence was associated with lower odds of treatment success (OR 0.48, 95% CI: 0.22 - 0.94) and higher odds of loss to follow-up (OR 2.1, 95% CI: 1.03 - 4.7), adjusting for sex, age, education, income, and employment. Higher engagement scores were associated with higher odds of success (OR 2.2 times per standard deviation increase). Engagement with TB-TST was associated with improved TB treatment outcomes. Strategies to increase and sustain engagement, particularly among high-risk groups, may improve adherence and maximize DAT benefits.