Abstract: 【Abstract】 Objective To investigate the serological response and Treponema pallidum DNA （TP-DNA） levels in body fluids of patients with latent syphilis after treatment with benzathine penicillin. Methods Clinical data were collected from patients who were diagnosed with latent syphilis or early symptomatic syphilis and treated with benzathine penicillin at the Department of Dermatology, the Second Affiliated Hospital of Nanjing Medical University from August 2021 to December 2024. Patients who had completed 12 months of follow-up were included in the analysis. Peripheral blood samples were collected before treatment and at 3, 6, 9, and 12 months after treatment; the rapid plasma reagin （RPR） test was used to evaluate the serological response, and the results at 12 months were used to assess the final response. For patients with latent syphilis who voluntarily underwent body fluid testing, peripheral venous blood, saliva, and first-morning midstream urine samples were collected before treatment, and posterior fornix swab samples were additionally collected from female patients; real-time fluorescence-based quantitative PCR was performed to detect TP-DNA levels in samples. Multivariate logistic regression analysis was conducted to identify the factors influencing the serological response in patients with latent syphilis. Results A total of 420 patients with latent syphilis were included, comprising 195 males （46.4%） and 225 females （53.6%）, aged 18 to 84 （40.36 ± 17.09） years; among them, 147 （35.0%） were diagnosed with early latent syphilis and 273 （65.0%） with late latent syphilis. Thirty-eight patients with early symptomatic syphilis were included, comprising 26 males （68.4%） and 12 females （31.6%）, aged 18 to 68 （35.24 ± 13.77） years; among them, 15 （39.5%） were diagnosed with primary syphilis, and 23 （60.5%） with secondary syphilis. Among the patients with latent syphilis, 343 responded （106 cured and 237 with an effective response）, with a response rate of 81.7%; among the patients with symptomatic syphilis, 36 responded （8 cured and 28 with an effective response）, with a response rate of 94.7%. Univariate logistic regression analysis showed that age, disease stage, and initial RPR titers were associated with the 12-month serological response in patients with latent syphilis （all P < 0.05）; multivariate analysis showed that age ≥ 45 years and late syphilis were independently associated with poor prognosis （both P < 0.05）, and an initial RPR titer of 1∶16 to 1∶32 was independently associated with a favorable outcome （P < 0.001）. Among the 26 patients with latent syphilis who voluntarily underwent body fluid testing, the positive rate of TP-DNA was the highest in sera （11/26, 42.3%）, followed by saliva （8/26, 30.8%）, vaginal swabs （3/16, 18.8%）, and urine （4/26, 15.4%）. Conclusions Patients with latent syphilis had a relatively low serological response rate to benzathine penicillin treatment. Age ≥ 45 years and late latent syphilis were independent influencing factors for a poor response. TP-DNA could be detected in the body fluids of patients with latent syphilis, suggesting a potential risk of transmission.

Key words: Syphilis, latent, Treponema pallidum, Penicillin G benzathine, Rapid plasma reagin test, Serological response