Project Summary Marginalized populations such as women who use drugs (WWUD) have elevated risk of COVID-19 with risk mitigation techniques owing to the social nature of drug use procurement, drug use and sex work. High rates of structural vulnerabilities (e.g., homelessness, hunger, incarceration) in combination with low levels of healthcare utilization are key drivers of this high burden of disease. Through the “C2SPARC” study, we propose expanding the depth of our understanding of drivers of POCT uptake in both research and service delivery contexts. Specifically, we propose adding a 6-month follow-up visit (“C2SPARC visit”) to the CARE study to more robustly examine trends in POCT uptake over time. Secondly, in partnership with a leading harm reduction organization that serves WWUD, we propose designing and implementing POCT on their nighttime mobile outreach van that provides harm reduction (e.g., condoms, naloxone, syringes) and basic necessities (e.g., food, clothing). C2SPARC will employ Andersen’s Behavioral Model (Aim 1), PRISM (Practical, Robust, Implementation, and Sustainability Model) (Aim 2), and the Theoretical Framework of Acceptability (TFA) (Aim 3) to meet the following aims: 1) to examine predisposing (e.g., social - homelessness, food insecurity; individual - drug use, race/ ethnicity, health beliefs) factors as well as enabling (past COVID-19 testing, vaccine uptake) factors that predict uptake of POCT over a six-month period among WWUD (N=250) in Baltimore, Maryland; 2) to collaborate with the SPARC Center to develop and implement POCT on their mobile outreach van that primarily serves WWUD in Baltimore City, Maryland; and to examine the feasibility (e.g., testing uptake) and acceptability (e.g., participant burden, testing self-efficacy) of mobile POCT testing among WWUD (N=250) who are clients of SPARC outreach. C2SPARC is innovative its leverage of the Phase I cohort to evaluate POCT testing uptake longitudinally which will inform the implementation of COVID-testing in the context of a meaningful community partnership. Situating COVID testing in the context of trusted service provider is urgency needed. The study’s impact and sustainability will also be enhanced by a community advisory board (CAB). Study results can be quickly disseminated to policy makers and the target population through products (i.e., fact sheets, manuscripts) and events (i.e., community forums) to inform community-based testing and eventual vaccination programs targeting WWUD and similarly marginalized populations.