Introduction/objectives: Undetectable = Untransmittable (U = U) means that virally suppressed HIV-positive partners cannot transmit HIV. With advancements in HIV care and the increasing number of mixed HIV-status relationships, we quantified U = U agreement (agreeing/disagreeing that U = U is true) among people in mixed HIV-status relationships, assessed response concordance between partners, quantified the association between dyad-level U = U agreement and condomless sex, and estimated interaction effects of viral suppression.
Methods: A cross-sectional opportunistic and snowball sampled survey explored condom use, U = U agreement, viral suppression, sociodemographic/relationship characteristics, and sexual behavior among 306 participants (153 matched dyads) in mixed HIV-status relationships (2016-2018). Bivariate analyses identified sociodemographic/relationship characteristics associated with U = U agreement. Cohen's Kappa assessed response concordance between partners. Firth logistic regression estimated associations between dyad-level U = U agreement and condomless sex with effect modification by viral suppression.
Results: Of 293 responses to the U = U question, 53.2% agreed with U = U. Agreement was associated with younger age (p = 0.006) and shorter duration of HIV in relationships (p = 0.034). Concordance between partners was higher for factual questions (kappa>0.50) and lower for belief/decision-making questions (kappa<0.40). The predicted probability of always having condomless sex was 0.60 (95% CI:0.57,0.64) when dyads agreed with U = U and the HIV-positive partner was virally suppressed. The likelihood of always having condomless sex was low when the HIV-positive partner was not virally suppressed, whether or not dyads agreed with U = U (predicted probability range: 0.08;95% CI:0.06,0.11 to 0.25;95% CI:0.17,0.33), or when only one partner agreed with U = U (predicted probability range:0.02;95% CI:0.01,0.02 to 0.11;95% CI:0.07,0.15).
Conclusions: Dyad-level U = U agreement, viral suppression, and views of both partners were key factors in mixed HIV-status couples' decisions to have condomless sex. Future representative studies among sexual identity and racialized minority sub-populations are needed to better understand how mixed HIV-status relationships receive and apply U = U messaging, with a focus on partner age and the duration of HIV within relationships.
Copyright: © 2025 Xi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.