Syphilis Positivity Among Men Who Have Sex With Men With Direct, Indirect, and No Linkage to Female Sex Partners: Exploring the Potential for Sex Network Bridging in Baltimore City, MD.

Background: Syphilis epidemics among women and men who have sex with men (MSM) may be connected, but these connections are poorly understood. Using egocentric network data from a US urban MSM cohort, we examined sociodemographics, behaviors, and syphilis positivity among MSM with (1) direct (MSM who report sex with women, MSMW); (2) indirect (MSM who only report male partners, some of whom are MSMW, MSMO/W); and (3) no (MSM who only report male partners and whose partners only have sex with men, MSMO/O) connection to women.

Methods: Sexually active MSM aged 18 to 45 years were administered behavioral and network interviews (recall period: 3 months) and syphilis/HIV testing. Syphilis positivity was defined as rapid plasma reagin titer ≥1:8. Modified Poisson regression was used to test for differences across groups.

Results: Among 385 MSM, 14.5% were MSMW and 22.3% were MSMO/W. MSMW and MSMO/W were significantly more likely than MSMO/O to report sex behaviors associated with increased syphilis acquisition/transmission risk, including ≥2 sex partners (MSMW: adjusted prevalence ratio [aPR], 1.28 [0.98-1.68]; MSMO/W: aPR, 1.35 [1.09-1.69]) and concurrent sex partners (MSMW: aPR, 1.50 [1.17-1.92]; MSMO/W: aPR, 1.39 [1.11-1.74]), and for MSMW only, transactional sex (aPR, 2.07 [1.11-3.88]). Syphilis positivity was 16.4% and was lower among MSMW (9.4%) and MSMO/W (14.1%) than MSMO/O (18.5%), but differences were not significant.

Conclusions: There may be considerable connectivity between MSM and female sex partners that could facilitate syphilis transmission, and behaviors that increase acquisition/transmission risk among MSMW and MSMO/W may be distinct from MSMO/O. Future work should focus on examining the context and temporal patterns of sex partnerships among MSMW and MSMO/W.