Changes in Substance Use and Sexual Behaviors Following an STI Diagnosis among a Cohort of MSM in Los Angeles, CA.

<bold>Background: </bold>Sexually transmitted infections (STIs), STI reinfection, Human Immunodeficiency Virus (HIV) acquisition and changes in behaviors following an STI were examined in a cohort of men who have sex with men (MSM) in Los Angeles, CA.<bold>Methods: </bold>Data from a longitudinal study of MSM enrolled from 2014 with at least one follow-up visit through March 2020 were analyzed (n = 447; 1,854 visits). Study visits every 6 months included self-interviews for sexual behaviors, substance use, and specimen collection for chlamydia, gonorrhea, syphilis, and HIV testing. Changes in behaviors were assessed using McNemar's test and participants not diagnosed with an STI served as controls for a difference-in-differences (DiD) analysis of changes over time.<bold>Results: </bold>Cumulative incidence of an STI was 55% (248/447). At 24-months post STI diagnosis methamphetamine use declined from 50% to 35% (p < .01), and median number of sex partners declined from 5 (IQR: 2-11) to 2 (IQR: 1-6)(p < .01). Among participants at risk for HIV and diagnosed with an STI (n = 102), PrEP use was 35% and HIV-seroconversion was 6%. Based on DiD analyses, participants diagnosed with an STI had higher levels of substance and higher number of sex partners when compared to those with no STIs, however, declines in these behaviors were comparable to participants not diagnosed with an STI (pDID > 0.05).<bold>Conclusions: </bold>Despite behavior modifications following an STI diagnosis, STI/HIV incidence was high, suggesting that MSM with STIs occupy sexual networks where reductions in sexual and substance using behaviors do not protect them from ongoing exposure to STIs and HIV. [ABSTRACT FROM AUTHOR]