'… if U equals U what does the second U mean?': sexual minority men's accounts of HIV undetectability and untransmittable scepticism.

The everyday meaning and use of HIV 'undetectability' raises significant questions about the social and sexual significance of this state of viral suppression. We conducted in-depth, semi-structured interviews with 25 sexual minority men living in Vancouver, Canada, including men living with HIV. Interviews were audio-recorded, transcribed verbatim and analysed using grounded theory. Most participants understood being undetectable to signify that someone living with HIV is at a 'low,' 'lower,' or 'slim to no' risk of sexually transmitting HIV, as opposed to meaning 'uninfectious' or 'untransmittable'. Men discussed how undetectability was communicated in-person and online, including via sexual networking apps, and revealed how it is sometimes confused or conflated with another biomedical advance in HIV-prevention, namely pre-exposure prophylaxis (PrEP). HIV-negative men expressed significant scientific scepticism, a reluctance to incorporate a partner's low viral load or undetectable HIV status into their sexual decision-making, and an enduring fear associated with knowingly having sex with someone who is HIV-positive. We describe this as a form of . While international campaigns have worked to communicate the scientific message that 'undetectable equals untransmittable' (U = U), the sexual stigma attached to HIV remains durable among some gay, bisexual, queer and other men who have sex with men.