Brief Report: Sexual Mixing Patterns by HIV Status and PrEP Use Among Men Who Have Sex With Men Partnerships in Melbourne, 2011-2018

Background: Sexual mixing between HIV-positive, HIV-negative, and pre-exposure prophylaxis (PrEP) users among men who have sex with men (MSM) is an important determinant of the incidence of infection. There have been very limited studies examining the patterns of sexual mixing in relation to HIV status and PrEP use in the era of PrEP. Setting: Melbourne Sexual Health Centre (MSHC), Australia. Methods: We included all MSM partnerships attending MSHC on the same day between 2011 and 2018. A chi-square trend test was used to examine the changes in the annual proportion of partnerships by HIV serostatus in 2011-2018 and by PrEP use in 2016-2018. Results: Of the 1765 MSM partnerships who attended MSHC between 2011 and 2018, 1.3% of the partnerships were concordant HIV-positive, 91.0% were concordant HIV-negative, and 7.6% were HIV-discordant. The proportion of HIV-discordant partnerships increased from 0% in 2011 to 12.5% in 2018 (p(trend) < 0.001). In 2016-2018, only a small proportion (1.2%) of concordant HIV-negative partnerships involved both men taking PrEP, whereas 6.0% involved at least one man taking PrEP. Overall, 79.1% of concordant HIV-negative partnerships were not protected against HIV (ie, neither man taking PrEP), and this proportion declined significantly from 84.3% in 2016 to 74.0% in 2018 (p(trend) = 0.001). Conclusions: The pattern of sexual mixing by HIV status and PrEP use among MSM partnerships has changed over time. PrEP use in both men within MSM partnerships is not common. About 79% of concordant HIV-negative partnerships were not protected against HIV as neither man taking PrEP.