Factors Associated with Syphilis Acquisition Among HIV-Infected MSM on Antiretroviral Therapy

Background:Syphilis is a re-emerging sexual transmitted infection among HIV-infected Thai men having sex with men (MSM) in Bangkok. We assessed factors associated with acquiring syphilis and risk behaviors among patients with positive syphilis serology in our HIV cohort in Bangkok, Thailand.  

Methods:Screening tests, VDRL and Architect Syphilis TP (Abbott), were performed. Self-assessment questionnaire on the history of sexually transmitted infections (STIs) and risk behaviors including condom use, substance abuse and alcohol intake was administered during August 2011-2012. Syphilis cases were compared between MSM and heterosexual men.  

Results:From a total of 1110 screened subjects, 649 were male (275 MSM, 374 heterosexual men), 127 (11.4%) were positive for syphilis screening (73 MSM and 30 heterosexual men), 36.4% had a history of STIs and only 47.3% had history of known or diagnosed syphilis infection in the past. The prevalence of syphilis among MSMs and heterosexual men were 26.5% and 8%, respectively. Compared to heterosexual men, MSM were younger (39 vs. 46 years), had a higher educational level and shorter duration of known HIV, and fewer HCV co-infection (1.9% vs 8.4%) and were living alone (85.7% vs. 25%). High titers of VDRL (≥ 1:8) were found in 55.6% of the MSM with positive VDRL. MSM were significantly at risk for acquiring syphilis (p<0.001) with an RR of 5.07 (95%CI: 3-8.5) by multiple logistic regression. Older age, no regular sexual partner and HBV co-infection were also significantly associated with syphilis acquisition among MSMs [RR(95%CI): 0.81 (0.73-0.9), 17.43 (3-101.15)and 14.93 (1.3-170.7), respectively].  

Conclusions:High titer of syphilis was prevalent among HIV-infected men in our cohort. Frequent syphilis screening is required among HIV-infected MSM at risk of acquiring syphilis. Regular condom use should strongly be encouraged to prevent STIs.