Awareness and Acceptability of Undetectable = Untransmittable Among a U.S. National Sample of HIV-Negative Sexual and Gender Minorities.

While the "Undetectable = Untransmittable" (U=U) message is widely endorsed, little is known about its breadth and reach. Our study describes socio-demographic characteristics and sexual behaviors associated with having heard of and trusting in U =U in a U.S. national sample of HIV-negative participants. Data were derived from the Together 5,000 cohort study, an internet-based U.S. national cohort of cis men, trans men and trans women who have sex with men. Approximately 6 months after enrollment, participants completed an optional survey included in the present cross-sectional analysis (n = 3286). Measures included socio-demographic and healthcare-related characteristics; questions pertaining to knowledge of and trust in U=U (dependable variable). We used descriptive statistics and multivariable logistic models to identify characteristics associated with these variables and explored patterns in willingness to engage in condomless anal sex (CAS) with regard to trust in U=U. In total, 85.5% of participants reported having heard of U=U. Among those aware of U=U, 42.3% indicated they trusted it, 19.8% did not, and 38.0% were unsure about it. Latinx, Asian, lower income, and Southern participants were less likely to have heard of U=U. Having had a recent clinical discussion about PrEP or being a former-PrEP user were associated with trust in U=U. Willingness to engage in CAS was positively associated with trust in U=U, and varied based on the partner's serostatus, PrEP use and viral load. Although we found high rates of awareness and low levels of distrust, our study indicated that key communities remain unaware and/or skeptical of U=U.