Grant: Travel Awards - Institute Community Support

Background: Infectious syphilis has reemerged as a global public health threat. Since 2013, the incidence of infectious syphilis in Ontario, Canada has surged by 345%, alongside significant demographic shifts. We evaluated intersecting risk factors associated with seropositivity in an equity-deserving population in Ontario. Methods: We used data from the Syphilis Point of Care Rapid Test and Immediate Treatment Evaluation (SPRITE) study- a community-based study across eight Ontario public health units (PHUs). Sociodemographic and risk factor data such as being un(der)housed, using drugs (PWUD), or engaging in survival sex work, was collected from public health intake forms along with lab-based syphilis testing. Syphilis seroprevalence, which indicates a current or previous syphilis infection, was calculated by risk factor to estimate the number of syphilis cases among those using drugs or who are un(der)housed. Results: From April-November 2024, 407 participants were included: median age 38; 42% female; 62% un(der)housed; 34% reported a sexual risk factor; 63% PWUD, 47% of whom used crystal meth. Syphilis seroprevalence was 7.6%. It was significantly higher among women and PWUD. Crystal meth use was independently associated with seropositivity compared to other illicit drugs. Seropositivity was highest at 19.2% among participants who reported having sexual risk factors, PWUD, and being un(der)housed. Conclusion: Syphilis burden is heightened at the intersection of sexual risk factors, illicit drug use, and housing instability among equity-deserving populations. This signals a significant shift in Ontario's syphilis epidemiology, highlighting the urgency of developing targeted prevention, screening, and intervention strategies to address the unique needs of this population.