Growing Acceptability of Undetectable = Untransmittable but Widespread Misunderstanding of Transmission Risk: Findings From a Very Large Sample of Sexual Minority Men in the United States.

BACKGROUND: Several studies have demonstrated no linked HIV transmissions in serodifferent sexual encounters where the partner with HIV has an undetectable viral load. As a result, awareness and dissemination of treatment as prevention, and movements such as "Undetectable = Untransmittable" (U = U), has grown. SETTING: We conducted an online cross-sectional survey from November 2017 through September 2018 to gather data from a total of 111,747 sexual minority men (SMM) in the United States. METHODS: Participants provided sociodemographic data and answered questions regarding biomedical status, HIV and STI prevention behaviors, drug use, condomless anal sex, and perceived accuracy of the U = U message. We conducted analyses to understand factors associated with perceived accuracy of U = U stratified by HIV status. RESULTS: Overall, 53.2% of the sample perceived U = U as accurate, with the highest rates among HIV-positive SMM (83.9%), followed by HIV-negative (53.8%) and status-unknown (39.0%) SMM. Multivariable models showed accuracy beliefs were, on average, 1-2% higher for each consecutive month of recruitment. Consistent with previous work, there was greater heterogeneity among HIV-negative and unknown men, with several factors differentiating perceived accuracy, compared with SMM with HIV. Perceived transmission risk levels with undetectable partners were skewed well above accurate levels, and greater perceived transmission risk was associated with lower perceived accuracy of U = U. CONCLUSIONS: Public confidence in treatment as prevention and U = U is growing, but clear, unequivocal messaging about the effectiveness of U = U is critical. Owing to misunderstandings of risk, language that focuses on protective benefits rather than transmission risks may reach more people and allow for better comparisons with PrEP and condoms.