Aims: To test the acceptability and feasibility of ecological momentary assessment (EMA) of mood and injection risk behavior among young people who inject drugs (PWID), using mobile phones. Methods: Participants were 185 PWID age 18-35 recruited from two sites of a large syringe service program in Chicago. After completing a baseline interview, participants used a mobile phone app to respond to momentary surveys on mood, substance use, and injection risk behavior for 15 days. Participants were assigned to receive surveys 4, 5, or 6 times per day. Results: Participants were 68% male, 61% non-Hispanic white, 24% Hispanic, and 5% non-Hispanic Black. Out of 185 participants, 8% (n = 15) failed to complete any EMA assessments. Among 170 EMA responders, the mean number of days reporting was 10 (SD 4.7), the mean proportion of assessments completed was 0.43 (SD 0.27), and 76% (n = 130) completed the follow-up interview. In analyses adjusted for age and race/ethnicity, women were more responsive than men to the EMA surveys in days reporting (IRR = 1.33, 95% CI 1.13 1.56), and total number of surveys completed (IRR = 1.51, 95% CI 1.18-1.93). Homeless participants responded on fewer days (IRR = 0.76, 95% CI 0.64-0.90) and completed fewer surveys (IRR = 0.70, 95% CI 0.54-0.91), and were less likely to return for follow-up (p = 0.016). EMA responsiveness was not significantly affected by the number of assigned daily assessments. Conclusions: This study demonstrated high acceptability and feasibility of EMA among young PWID, with up to 6 survey prompts per day. However, homelessness significantly hampered successful participation.
