Introduction Syphilis infection rates began an upward trend in the late 1990s, disproportionally affecting men who have sex with men (MSM). Many of these MSM were co-infected with Human Immunodeficiency Virus (HIV). Co-infection often results in a significantly higher burden of disease. Little data examine the prevalence of syphilis in Brazil, the largest country of Southern America. The purpose of this study is to examine disease prevalence and rates of syphilis and HIV co-infection among MSM in São Paulo, the most populous city in Brazil.

Methods This study analyses data from two separate surveys. The first study recruited 771 MSM at randomly selected venues where MSM congregate using time-location sampling (TLS) in 2011. HIV testing was done with all MSM in the field; Syphilis testing was done on a sub-sample of MSM (n=227) who presented to a specialty clinic for screening. The second study recruited MSM by peer referral through respondent-driven sampling (RDS) in 2016. All participants (n=338) were tested for HIV and syphilis. RDS and TLS weights were used in the analysis to provide data representative of the population of interest.

Results In 2011, 19.8% (CI 13.5–28.1) of MSM were positive for syphilis and 14.7% (CI 9.2–22.7) were positive for HIV, particularly affecting people within 35–49 years (representing 37% and 35% of the syphilis and HIV positive results, respectively). Among the MSM living with HIV, co-infection with syphilis was 45%. In 2016, 30.67% (CI 21.8–39.5) of MSM were positive for syphilis and 23.0% (CI 13.17–32.9) were positive for HIV. In the MSM living with HIV, 48% tested positive for syphilis. In a Poisson regression, the risk for HIV and Syphilis is higher for 2016.

Conclusion HIV and Syphilis prevalences are at high levels among MSM sampled in São Paulo. An alarming majority of MSM with HIV tested positive for syphilis in 2016. Interventions promoting frequent STI screening among HIV-positive and negative MSM are needed to address both epidemics and mitigate the adverse health outcomes of co-infection and to prevent onward transmission.