Background: Syphilis prevalence continues to be high among at-risk populations such as men who have sex with men (MSM). In low and middle-income countries, syphilis remains a neglected epidemic with a lack of effective prevention strategies.
Methods: PICASSO is a clinic-based study of MSM in Lima, Peru that includes behavioral surveys and syphilis testing with rapid plasma reagin (RPR) titers (BD Macro-Vue RPR, Becton-Dickinson, NJ) and Treponema pallidum Particle Agglutination (Serodia TP-PA, Fujirebio Inc, Japan). Participants with recent syphilis infection (RPR titer ≥1:16) were compared to participants with non-reactive titers. Participants with RPR titers 1:1-1:8 were excluded. Age in years was analyzed as a continuous variable. HIV perceived risk was self-reported on a 4-point scale. Factors associated with recent syphilis were explored using Poisson regression to compute risk ratios (RR).
Results: The frequency of recent syphilis infection was 26/171 (15.2%). More individuals with recent syphilis infection were HIV-infected; 6/26 (23.0%) compared to 18/91 (19.8%) participants with nonreactive RPR titers (RR 1.16, p = 0.711). Recent syphilis infection was associated with younger age (RR 0.95, p =0.016) and higher self-perceived risk of HIV (RR 1.33, p =0.06). Insertive anal sex was associated with a lower relative risk of recent syphilis infection (RR 0.25, p = 0.05) compared to receptive or versatile. Other sexual behaviors, substance use and alcohol use were not associated with recent syphilis infection.
Conclusions: Recent syphilis infection was common in the clinic-based sample of high-risk MSM. Frequent syphilis and HIV co-infection suggest an integrated strategy is necessary for prevention and treatment efforts. Our findings suggest that patterns of syphilis transmission are only partially explained by current measures of behavioral risk.