Previous research has discussed the serological response to syphilis treatment [8,9,10,11, 14]. The time point used in the analysis is important when assessing the treatment effect, and a relatively wide window of time is recommended for determining serologic responses . Compared with previous studies, each participant included in the final analysis received a 2-year follow-up, which provided more sufficient information to determine their outcomes. We report an overall rate of 10.94% among first-diagnosed patients, and the figures for the MSM population and HIV-infection patients were much higher. Therefore, it is very important to perform regular clinical and serologic evaluations after treatment, especially for the high-risk populations. To the best of our knowledge, this is the first study in China to detect the treatment failure and reinfection rate among STD clinic patients after long term follow-up.
We identified three potential associated factors with the treatment failure and reinfection in this study. The finding supports the findings of other investigations that also demonstrated that HIV- infected patients with syphilis might be more likely to experience serological failure and reinfection compared to non-HIV infected patients [17,18,19]. We speculate that HIV-infected patients with more immunosuppression might respond with a low rate to effective treatment. In addition, HIV might accelerate and change the clinical course of syphilis, and this co-infection could increase the incidence of the complications of syphilis [16, 20, 21]. Furthermore, HIV makes it more likely for syphilis to present with non-typical features . For example, a UK enhanced surveillance program reported on the presentation of syphilis both in HIV-negative and HIV-positive men. Primary syphilis was diagnosed in 42 and 27%, and secondary disease was diagnosed in 40 and 58% of HIV-negative and HIV-positive patients, respectively . Therefore, it is important for medical practitioners to be aware of how syphilis might present in patients with underlying HIV infection and the implications for treatment and follow-up.
We also found that secondary syphilis patients are more likely to experience treatment failure or reinfection compared with primary syphilis patients. Although there are no concrete indications regarding the different stages, and the clinical stages of syphilis often overlap, this finding highlights the importance of early diagnosis and treatment. Furthermore, the frequency of condom use was found to be associated with the response to treatment. Patients might be linked to recurrent exposure of syphilis from their sexual networks through unprotected sexual activity . Patients who practice safe sex are less likely to be re-exposed to risky partners. Unprotected sexual behaviors, therefore, increase the likelihood of experiencing treatment failure or reinfection. This finding suggested that health counseling and safety education on sex activity should be intensified to increase condom use, especially among high risk populations.
Our study has several limitations. First, selection bias is possible because 28% of patients were excluded due to lack of data or loss of follow-up. If the exclusion of these patients affected the outcome is unknown. Second, some information collected at baseline is retrospective, such as the number of sex partners and the frequency of condom use, which might not reflect the actual conditions during the follow-up. In addition, a relatively rough classification was adopted in this study. We combined serological cure and serofast together. We did not distinguish patients with treatment failure or reinfection in the analysis, so it is hard to make a distinction without information regarding their exposure and network. Furthermore, the bivariate analysis used for the first-step variable selection might be not biologically plausible all of the time. Additionally, the results from one city might be not well generalized to other regions. However, we believe this study provides a good representation of southeast coastal cities, and more studies in diverse areas are needed in further research.