Syphilis positivity among men who have sex with men (MSM) 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 U.S. urban MSM cohort, we examined socio-demographics, 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 18-45 years were administered behavioral and network interviews (recall period: three months) and syphilis/HIV testing. Syphilis positivity was defined as RPR 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 aPR:1.28 (0.98-1.68); MSMO/W aPR:1.35 (1.09-1.69)], 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.
Competing Interests: Conflicts of Interest and Sources of Support: This work was supported by the Centers for Disease Control and Prevention [1U01PS005171-01], and the Johns Hopkins University Center for AIDS Research [P30AI094189].
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