Quantifying Population-Level Sexual Mixing by HIV Status and Pre-Exposure Prophylaxis Use Among Men Who Have Sex with Men: Implications for Combination HIV Prevention

Abstract

Background: Sexual mixing patterns influence HIV transmission dynamics. We quantified the population-level sexual mixing by two attributes (HIV status and pre-exposure prophylaxis (PrEP) use). Methods: We used data from Engage-Montreal (2017-2018), a cross-sectional survey of men who have sex with men (MSM) ≥16 year-old recruited using respondent-driven sampling. MSM with ≥1 anal/oral sex partners in the past 6 months (P6M) reported their own and partners' HIV status and PrEP use. Within P6M-partnerships across all MSM, we compared observed seroconcordance to what would have been expected by chance under proportionate mixing-if zero individual serosort. Within recent partnerships where both individuals were HIV-negative, we compared observed concordance in PrEP use at last sex to that expected by chance. We used chi-squared tests for comparisons, and calculated the excess fraction of concordance beyond chance. Findings: Of the 11,883 P6M-partnerships by 1137 respondents, 56.3% comprised partners' of known-status. Compared with by chance and among partners of known-status, HIV-positive respondents (n=207) had a higher proportion of HIV-positive partners (66.4% vs. 23.9%; p<0.001); both HIV-negative (n=831) and respondents of unknown-status (n=99) had higher proportions of HIV-negative partners (87.9%, and 92.7%, respectively, vs. 76.1%; p<0.001). HIV-negative respondents on PrEP had a higher proportion of HIV-positive partners than those not on PrEP (17.1% vs. 9.3%; p<0.001). They also had a higher proportion of partners on PrEP among their HIV-negative partners compared with by chance (50.6% vs. 28.5%; p<0.001). Excess fractions of seroconcordance beyond chance were 64.0%, 8.9%, and 10.7% for HIV-positive, HIV-negative on PrEP, and HIV-negative not on PrEP MSM, respectively. The excess fraction of concordance in PrEP use beyond chance was 43.7%. Interpretation: The high degree of population-level serosorting and PrEP matching, and the influence of PrEP on sexual mixing patterns should be considered in the implementation of PrEP within the context of combination HIV prevention. Funding: Canadian Institutes of Health Research [TE2-138299, CTN-300, FN-13455]; Canadian Foundation for AIDS Research [Engage]; Canadian Blood Services [MSM2017LPOD]; Ontario HIV Treatment Network [1051]; Ryerson University; and Public Health Agency of Canada [4500370314]. Declaration of Interest: No conflict of interest to declare. Ethical Approval: The following institutional ethics review boards approved the study: Ryerson University, St. Michael’s Hospital, University of Toronto, University of Windsor, University of British Columbia, University of Victoria, the Simon Fraser University, and the Research Institute of the McGill University Health Centre.