Implementing and retaining a large-scale technology-mediated cohort to study HIV incidence and PrEP uptake among vulnerable cisgender men as well as transgender individuals in the U.S., the Together 5,000 cohort.

HIV remains a significant public health concern requiring innovative solutions. Widespread internet access and advancing health technologies (e.g., home-based HIV/STI testing) have often made research and intervention implementation more efficient and effective. The purpose of this analysis is to describe a technology-mediated HIV prevention cohort's implementation, participant engagement strategies, and methods to overcome study retention challenges. Participants residing in the U.S. or territories were recruited from geospatial social networking applications between October 2017 - June 2018. Enrolled participants completed annual online surveys and at-home HIV testing-baseline, 12-, 24-, 36-, 48-months follow-up. Multiple adjusted logistic regression models were used to determine sociodemographic and behavioral characteristics associated with completing each survey and returning a HIV specimen collection kit. Study response probability weights were calculated to account for attrition. Results suggest several sociodemographic and behavioral characteristics were associated with completing study activities. Importantly, participants who were Black had lower odds of completing surveys and HIV testing. This cohort demonstrated feasibility for recruiting and retaining a cohort of 5,000 HIV-vulnerable individuals and identified 569 HIV infections. Our findings highlight many benefits of conducting internet-mediated studies; however, these studies face unique challenges that may require post-hoc analytic solutions or effective retention strategies.