Recruiting vulnerable populations to participate in HIV prevention research: findings from the Together 5000 cohort study.

<bold>Purpose: </bold>The aim of the article was to examine factors associated with completing enrollment milestones in the Together 5000 cohort of at-risk men (n = 8661), transmen (n = 53), and transwomen (n = 63) who have sex with men.<bold>Methods: </bold>Between 2017 and 2018, participants completed an online enrollment survey and were offered opportunities to complete an incentivized secondary online survey as well as self-administered at-home HIV testing (OraSure). We explored factors associated with completing each study component.<bold>Results: </bold>In total, 8777 individuals completed our enrollment survey, 6166 (70.3%) completed the secondary survey, and 5010 returned the at-home HIV test kit that was mailed to them (81.3% of those mailed a kit). In our multivariable models, those who were White, with more years of education, were more likely to complete study components, although the magnitude of these associations was small. For example, 50.9% of those enrolled, 47.9% of those completing the secondary survey, and 46.8% of those completing HIV testing were persons of color-a statistically significant, but meaningfully insignificant decline.<bold>Conclusions: </bold>These findings highlight the need for researchers to identify barriers that may prevent persons of color and younger individuals from participating in research studies. [ABSTRACT FROM AUTHOR]