Syphilis re-infection in high-risk men and women in 3 cities in Peru, 2003-2007

Background Syphilis infection is endemic among men who have sex with men (MSM) and other high-risk groups in developing countries, but the epidemiology of syphilis re-infection is poorly understood.  We characterized factors associated with syphilis re-infection in a high-risk cohort in Peru.

Methods Participants in the NIMH CPOL trial were assessed at baseline and two annual follow-up visits with HIV/STI testing and behavioral surveys  All participants underwent syphilis testing with RPR screening and TPPA confirmation and participants diagnosed with syphilis referred to 4- and 9-month follow-up visits. Antibiotic treatment was provided according to CDC guidelines. Re-infection was defined as a 4-fold titer increase or recurrence of seroreactivity after successful treatment. Chi-square was used for bivariate associations and discrete time proportional hazards regression yielded adjusted hazard ratios (HR) for longitudinal analysis.

Results  Of 3301 participants, 216(6.5%) were RPR/TPPA-positive (median1:8, range1:1-1:1024). Syphilis re-infection was identified in 100/216(46.3%); of those 100, 27/67(40.3%) were heterosexual high-risk men, 7/15(46.7%) high-risk women and 60/134(44.8%) MSM (p-value>.05). In the behavioral longitudinal analysis, visiting a doctor within the last 6 months (HR0.65, 95%CI 0.44-0.97) reduced risk of re-infection and substance use before sex (HR1.68, 95%CI 1.15-2.47) increased risk. Clinically, diagnosis of re-infection was more common among participants who completed all required follow-up visits (HR1.57, 95%CI 1.05-2.37).

Conclusions  Syphilis re-infection in Peru is high among high-risk groups including, but not exclusive to, MSM. More frequent monitoring can improve detection of occurrences of re-infection. Further studies are needed to further define patterns of syphilis re-infection and associated risk factors.