Brief Report: Syphilis Incidence and Effect on Viral Load, CD4, and CD4/CD8 Ratio in a Thai Cohort of Predominantly Men Who Have Sex With Men Living With HIV.

Background Syphilis has been increasing in the past years, especially among men who have sex with men (MSM). The aim of the study was to assess syphilis prevalence and incidence and changes in CD4 count and viremia in the RV254 cohort of persons living with HIV who initiated antiretroviral therapy during acute HIV infection (AHI) in Bangkok, Thailand. Methods From 2009 to 2018, all cohort participants with AHI were tested for syphilis using a qualitative treponemal chemiluminescent microparticle immunoassay and rapid plasma reagin on enrollment, every 24-48 weeks thereafter and when clinically indicated. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for factors associated with incident syphilis. Results Among 579 participants, the median age was 26 (interquartile range: 22-31) years and 564 (97.4%) were men. Syphilis prevalence at enrollment was 14.3% and incidence was 10.2 cases per 100 person-years. Participants with syphilis were more likely to be MSM (HR 3.68, 95% CI: 1.16 to 11.62), use methamphetamine (HR 2.31, 95% CI: 1.51 to 3.54), and have hepatitis C (HR 2.63, 95% CI: 1.59 to 4.34). HIV RNA >50 copies/mL occurred in 6 (3.9%) participants at incident syphilis diagnosis and in 6 (3.9%) after syphilis treatment. Median CD4 count (cells/mm3) declined from 663 before syphilis to 624 at syphilis diagnosis (P = 0.07), rising again to 660 after syphilis treatment. Conclusion Syphilis was common in the RV254 cohort, inducing a marginal but significant impact on HIV RNA and a temporary decline in CD4. Syphilis screening and behavioral risk reduction counseling should be implemented for MSM with AHI in Thailand.