TREATMENT UTILIZATION DURING COMMUNITY REENTRY OF OPIOID USE DISORDER INPATIENTS - PROJECT SUMMARY/ABSTRACT NEARLY 400,000 PEOPLE WITH AN OPIOID USE DISORDER (OUD) RECEIVE OUD TREATMENT EACH YEAR (19.7% OF ALL PEOPLE WITH AN OUD). COMMUNITY RE-ENTRY FOLLOWING RESIDENTIAL OUD TREATMENT IS A CRITICALLY VULNERABLE TIME, AS RISK OF RETURN TO USE, OVERDOSE, AND DEATH ARE INCREASED IN THE 30 DAYS FOLLOWING DISCHARGE. CONTINUITY OF CARE DURING RE-ENTRY IS VITAL IN SUPPORTING RECOVERY OUTCOMES, BUT LITTLE IS KNOWN ABOUT TREATMENT UTILIZATION DURING THIS HIGH-RISK PERIOD. INDIVIDUAL AND SOCIO-STRUCTURAL FACTORS CAN INFLUENCE TREATMENT UTILIZATION; HOWEVER, THERE IS A DEARTH OF INFORMATION REGARDING THE FACTORS THAT PREDICT TREATMENT UTILIZATION DURING RE-ENTRY. CHARACTERIZING TREATMENT UTILIZATION AND IDENTIFYING PREDICTORS OF TREATMENT ENGAGEMENT IS NECESSARY TO DETECT THOSE WHO ARE AT RISK FOR NOT ENGAGING WITH TREATMENT DURING COMMUNITY RE-ENTRY AND THUS ADDRESS CRITICAL GAPS IN THE OUD TREATMENT PIPELINE. BY DEFINING TREATMENT BROADLY, INCLUSIVE OF HARM REDUCTION STRATEGIES, AND COMBINING INTENSIVE LONGITUDINAL METHODS (ECOLOGICAL MOMENTARY ASSESSMENT [EMA]) WITH INNOVATIVE MACHINE LEARNING ANALYSES, THIS STUDY WILL BOTH CHARACTERIZE TREATMENT UTILIZATION WITH GREATER PRECISION AND IMPROVE PREDICTION OF TREATMENT ENGAGEMENT DURING COMMUNITY RE-ENTRY. OUR FINDINGS AIM TO IDENTIFY (IN RESIDENTIAL OUD TREATMENT) THOSE AT RISK FOR NOT ENGAGING WITH TREATMENT DURING COMMUNITY RE-ENTRY (TO INFORM PREVENTATIVE INTERVENTIONS) AS WELL AS TO PINPOINT PROXIMAL FACILITATORS AND BARRIERS TO TREATMENT UTILIZATION DURING COMMUNITY RE-ENTRY. THE PROPOSED SECONDARY DATA ANALYSIS AIMS TO CHARACTERIZE TREATMENT UTILIZATION AND IDENTIFY INDIVIDUAL AND STRUCTURAL FACILITATORS AND BARRIERS TO, AND PREDICTORS OF, OUD TREATMENT DURING COMMUNITY RE-ENTRY. THE TARGET POPULATION IS ADULTS WITH OUD WHO DISCHARGED FROM RESIDENTIAL OUD TREATMENT (N=150). THIS STUDY USES INNOVATIVE METHODS AND CUTTING-EDGE DATA ANALYSES TO MAXIMIZE EXISTING DATA FROM THE SPONSOR'S NIH-FUNDED STUDY (P20GM125507). AIM 1 USES EMA TO ACCURATELY AND RELIABLY DESCRIBE EXPERIENCES WITH TREATMENT UTILIZATION DURING COMMUNITY RE-ENTRY. AIM 2 APPLIES INNOVATIVE MACHINE LEARNING MODELING APPROACHES TO 1) SOCIO-STRUCTURAL AND CLINICAL DATA GATHERED DURING RESIDENTIAL TREATMENT TO IDENTIFY THOSE AT RISK FOR NOT ENGAGING WITH TREATMENT DURING COMMUNITY RE-ENTRY, AND 2) SYMPTOMS AND BEHAVIORS GATHERED DURING COMMUNITY RE-ENTRY WITH EMA TO IDENTIFY FACILITATORS AND BARRIERS TO TREATMENT UTILIZATION THE RE-ENTRY PERIOD. FINDINGS WILL INFORM CONTINUITY OF CARE, EVIDENCE-BASED TOOLS TO PREVENT AND/OR DELAY RETURN TO OPIOID USE, AND REDUCE HARMS ASSOCIATED WITH COMMUNITY RE-ENTRY. THIS PROPOSAL ADDRESSES CRITICAL GAPS IN MY TRAINING AND KNOWLEDGE AND WILL BE NECESSARY TO DEVELOP AN INDEPENDENT, NIH-FUNDED RESEARCH PROGRAM FOCUSED ON OPIOID USE AND OUD TREATMENT UTILIZATION DURING HIGH-RISK TRANSITIONAL PERIODS, SUCH AS COMMUNITY RE-ENTRY.