Variation in Syphilis Among Men who Have Sex with Men and Women in the United States and Association with Syphilis in Women

We aimed to evaluate the percentage of early syphilis (ES) cases in men who have sex with men (MSM) occurring in behaviorally-bisexual men (MSMW) in the US; determine how that percentage varies by race/ethnicity, region and over time; and to assess the relationship of measures of MSMW syphilis with syphilis rates in women. We used linear mixed-effects regression models to analyze aggregate 2013-2017 surveillance data from 16 US jurisdictions with high syphilis morbidity. Of all MSM ES cases, the mean percentage occurring in MSMW was stable over time at 11.5% but was higher in the South, and in Black men (P<0.01). The association between this percentage and race/ethnicity differed by region. Rates of all-stage syphilis in women were positively associated with the log number of MSMW cases per 100,000 men (P<0.01). Higher levels of syphilis morbidity among MSMW were associated with higher rates in women, and “bridging” may partially explain observed disparities. The interaction of race, region, and sex behavior and its implications within the current syphilis epidemic merit renewed focus.