The treatment outcome and predictors of serological response in syphilis in a sexually transmitted infections center, China.

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Serology is the mainstay for syphilis treatment monitoring. Baseline rapid plasma reagin (RPR) titre, HIV status, and syphilis stage have been found to be associated with the time to serological response among syphilis patients. This study mainly aims to evaluate the time to serological response, and to identify factors affecting the serological outcome. Medical records of syphilis cases diagnosed in Peking Union Medical College Hospital (PUMCH) between 2008 and 2018 were retrospectively reviewed. Kaplan-Meier analysis was performed to evaluate the median time to serologic response and cumulative probability of serologic response over time according to different variables. Cox regression model was conducted to find factors associated with serological response. There were 984 patients diagnosed with primary, secondary, or latent syphilis cases and receiving injections of benzathine penicillin G (BPG) as initial treatment at the Peking Union Medical College Hospital (PUMCH) between 2008 and 2018. Finally, data on 571 patients, including 49 (8.6%) primary syphilis, 261 (45.7%) secondary syphilis, and 261 (45.7%) latent syphilis, were used for analysis. It took longer time to achieve serological response for subjects aged ≥45years than younger individuals (89days versus 58days; p=0.008). Males achieved serological response more quickly than females (71days versus 83days; p = 0.011). There was a significant difference in the time to serological response according to different syphilis stages (p < 0.001), with 55days (95% CI, 43-67days) for primary, 57days (95% CI, 51-63days) for secondary, and 117days for latent syphilis. In addition, patients with lower baseline RPR titre had longer period to achieve serological response (252days [95% CI, 129-375days] for RPR titre ≤1:8, 78days [95% CI, 63-93days] for RPR titres from 1:16 to 1:32, and 53days [95% CI, 49-57days] for RPR titres ≥1:64, respectively; p<0.001). However, no significant difference in time to serological response to treatment was found according to HIV coinfection status. The result of multivariate Cox regression analysis showed that being older than 45years with latent syphilis, HIV coinfection, or with baseline RPR titre ≤1:8 was associated with slow response. Among patients followed for at least 1year or seroreverted, 128 (36.9%) had seroreverted within a year, and 219 (63.1%) still had a positive RPR after 1year. For multiple logistical regression, being female and HIV coinfection were significantly associated with the failure of seroreversion (OR, 0.42 [95% CI, 0.26-0.68]; p <0.001). This study revealed that younger age, higher initial RPR titre, early syphilis stage, and HIV-negative status were associated with faster serological cure. Female sex, individuals with HIV coinfection, and latent syphilis were significantly associated with the failure of seroreversion.