Comparisons of Serologic Responses of Early Syphilis to Treatment with a Single-Dose Benzathine Penicillin G Between HIV-Positive and HIV-Negative Patients

Poorer serologic responses of early syphilis to treatment have been inconsistently reported in HIV-positive patients compared with HIV-negative patients, but the interpretation of previous studies is limited by discrepant study designs. The present study aimed to evaluate the effect of HIV infection on the treatment response to a single dose of benzathine penicillin G (BPG) for early syphilis. From January 2015 to March 2020, adult patients with early syphilis who received a single dose of BPG were enrolled and rapid plasma reagin (RPR) titers were periodically determined. The primary outcome was serologic response, defined as at least a fourfold decline of RPR titer at 12 months of BPG treatment compared with that at baseline, which was examined in the intention-to-treat (ITT) and per-protocol analyses. Treatment failure included lack of at least a fourfold decline in RPR titers and at least a fourfold increase in RPR titers. We prospectively enrolled 184 HIV-positive and 68 HIV-negative participants with early syphilis, who were all men who have sex with men, with a higher proportion of previous syphilis (70.1%) and early latent syphilis (64.1%) among HIV-positive participants. In the ITT with last-observation-carried-forward analysis, HIV-positive participants had a significantly lower serologic response rate at 12 months of treatment than HIV-negative participants (73.4% vs. 91.2%). Of HIV-positive participants, 12.5% failed to achieve at least fourfold decline in RPR titers and 14.1% had at least a fourfold increase in RPR titers. The factors associated with 12-month serologic response were HIV infection (adjusted odds ratio [AOR] 0.33; 95% confidence interval [CI] 0.13–0.81) and RPR titer (per 1-log 2 increase, AOR 1.36; 95% CI 1.23–1.51). HIV-positive patients with early syphilis had poorer serologic responses to BPG treatment than HIV-negative patients during a 12-month follow-up period.