Objectives Men who have sex with men (MSM) and transgender women (TW) are highly vulnerable groups to sexually transmitted infections (STIs). This study aims to assess the prevalence of syphilis infection, sexual behaviour and identify factors associated with syphilis in MSM and TW in Campo Grande, Central Brazil.

Methods Between 2009 and 2011, 430 MSM/TW participants were interviewed and tested for syphilis. Univariable and multivariable regression analyses were done to assess associations with syphilis infection.

Results A total of 430 MSM/TW (278 MSM and 152 TW) were included in the study. The overall prevalence of lifetime syphilis and active syphilis was 34.7% (26.3% among MSM; 50.0% among TW) and 17.5% (12.3% among MSM; 27.0% among TW), respectively (p<0.001). In multivariable regression analysis, being 20–24 years and ≥30 years, having engaged in a variety of sexual practices and with a history of genital/anal ulcer in the last 12 months were associated with lifetime syphilis infection in the MSM group. Among TW participants, being ≥30 years of age, having more than 10 male sexual partners in last week and being infected with HIV were associated with lifetime syphilis. Factors associated with active syphilis among MSM were massage parlour/sauna recruitment and alcohol consumption at least once a week. Having sex with female partners in the past 12 months was predictive for active syphilis among TW.

Conclusions The prevalence of syphilis infection and risk sexual behaviour were high in the two samples, especially among TW. High levels of bisexual behaviours and low rates of consistent condom use indicate potential HIV/STIs transmission into the heterosexual population. This finding indicates the need and urgency for implementing more effective integrated programmes targeting MSM/TW for the prevention of syphilis and other STIs.