Prevalence of and Factors Associated with the Use of HIV Serosorting and Other Biomedical Prevention Strategies Among Men Who Have Sex with Men in a US Nationwide Survey.

PrEP and treatment-as-prevention (TasP) are biomedical strategies to reduce HIV transmission. Some men who have sex with men (MSM) are combining biomedical strategies with HIV serosorting-termed "biomed matching" when both partners are either on PrEP or TasP, or "biomed sorting" when one partner is using PrEP and the other TasP. Nevertheless, there is limited data on the extent of biomed matching/sorting in large geographically diverse samples. In 2016-2017, 5021 MSM from across the US were surveyed about their HIV status and HIV viral load/PrEP use, as well as that of their recent casual male partners. For each participant, we calculated the proportion of his partners who were (1) HIV-positive and undetectable, (2) HIV-positive and detectable/unknown, (3) HIV unknown/undiscussed, (4) HIV-negative on PrEP, (5) HIV-negative, not on PrEP. In total, 66.6% (n = 3346) of participants were HIV-negative and not on PrEP, 11.9% (n = 599) on PrEP, 14.1% (n = 707) HIV-positive and undetectable, 1.1% (n = 55) HIV-positive and viral load detectable/unknown, and 6.2% (n = 313) HIV unsure/unknown. A participant's own HIV and PrEP status/was significantly associated with that of his partners (all p < 0.001), evincing evidence of both serosorting and biomed matching. Among men on PrEP and those who were HIV-undetectable, there was also some evidence to suggest these participants dually engaged in biomed matching as well as biomed sorting. We found evidence of biomed matching and sorting, which may compound its effectiveness for those using it (i.e., both partners bring biomedical protection). Unintended consequences of biomed matching/sorting include that men not using a biomedical strategy may be less likely to benefit from a partner's use of the strategy-potentially further driving disparities in HIV infections. Public health campaigns might be well served to highlight not only the benefits that biomedical HIV prevention strategies provide for their users (e.g., "being on PrEP protects me from getting HIV"), but also the benefits that a user brings to his partners (e.g., "my use of PrEP means my partners won't get HIV"), and the benefits of being with a partner who is using a biomedical strategy (e.g., "my partner's use of PrEP/TasP protects me from HIV").