O3.2 - Rates of reported primary and secondary syphilis among men who have sex with men compared to men who have sex with women only and women who have sex with men in 37 US states, 2018

Background: Most reported primary and secondary (P&S) syphilis cases in the United States were among men who have sex with men (MSM) during 2010–2018. Because MSM are a minority population, this indicates a disproportionate burden of P&S syphilis among MSM. However, the magnitude of the disparity has not been quantified using population-standardized metrics such as rates. We compared rates of P&S syphilis between MSM, men who have sex with women only (MSW), and women who have sex with men (WSM) using new population estimates for 2018.

Methods: We used national case-based surveillance data on P&S syphilis reported through the National Notifiable Diseases Surveillance System for 2018, the most recent year that MSM population denominators were available. We limited our analysis to states with at least 70% complete reporting of sex of sex partners to reduce bias from missing data. Data were restricted to persons aged 18 years and older and were summarized by state, sex, and sex of sex partner(s). We calculated rates by dividing case counts by population estimates from previously published research, then calculated rate ratios (RRs) comparing MSM to MSW, MSM to WSM, and MSW to WSM for all eligible states, separately and combined.

Results: RRs were calculated for 37 states with sufficiently complete data. Among those states, RRs comparing MSM to MSW ranged from 40.5 (Oklahoma) to 365.1 (New Hampshire), with an overall RR of 85.9. RRs comparing MSM to WSM were greater but followed a similar geographic pattern, ranging from 50.4 (Oklahoma) to 684.5 (New Hampshire), with an overall RR of 120.0. Finally, RRs comparing MSW and WSM indicated greater similarity between them than between either group and MSM, ranging from 0.6 (Illinois) to 2.1 (Indiana), with an overall RR of 1.4.

Conclusion: This study quantified the disproportionate burden of P&S syphilis among MSM in the United States, with rates among MSM being at least 40 times those of either MSW or WSM across all states analyzed. These findings highlight the importance of targeted health interventions for syphilis as well as the necessity of population estimates for examining health disparities among sexual minority populations.