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PCR detection in diagnosis of early syphilis: a preliminary result from China
  1. Rui-Rui Peng1,2,
  2. Yue-Ping Yin1,3,
  3. Wan-Hui Wei1,3,
  4. Hong-Chun Wang1,3,
  5. Jin-Ping Zhang1,
  6. Xiang-Sheng Chen1,3
  1. 1Institute of Dermatology of Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing, China
  2. 2Shanghai Skin Disease Hospital, Shanghai, China
  3. 3National Center for STD Control, Nanjing, China
  1. Correspondence to Dr Xiang-Sheng Chen, National Center for STD Control, 12 Jiangwangmiao Street, Nanjing 210042, China; chenxs{at}

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Recently, Gayet-Ageron and colleagues published a systematic review and meta-analysis to evaluate the diagnostic values of Treponema pallidum PCR and concluded that PCR is a useful additional diagnostic tool.1 However, the data on examining diagnostic performance of PCR-based methods for early syphilis are still limited in China although a few studies with the indirect data from China were included in the literature review.1

During April to September 2009, we conducted a survey among patients with suspected primary or secondary syphilis recruited from an STI clinic in Nanjing, China, to evaluate the performance of PCR assay for early syphilis diagnosis. Following an ethical review by the Chinese Academy of Medical Sciences (CAMS) Institute of Dermatology, all eligible patients who agreed to participate in the survey were requested to be interviewed with a simple questionnaire and provide serum specimens for syphilis serological testing of treponemal (Treponema pallidum particle agglutination (TPPA)) and non-treponemal (toluidine red unheated serum test (TRUST)) antibodies and swab specimens for dark-field microscopy (DFM) and PCR detection of T pallidum. We used polA gene for PCR assay which has been verified and suggested by the US CDC.2

The response rate was 94.8% (110/116), and the median age of participants was 40 years with IQR of 30–47. Out of 110 participants, all provided venous blood, and 62 (56.4%) and 48 (43.6%) provided samples from chancres and condyloma lata, respectively. PCR had a higher positive rate than DFM (78.2%, 86/110 vs 67.3%, 74/110; χ2=6.722, p=0.008). However, PCR and serological test did not reach a significant difference (78.2%, 86/110 vs 76.4%, 84/110; χ2=0.125, p=0.727). We used combination of clinical sign, positive DFM and/or active serological test as reference criteria.3 The sensitivity and specificity of PCR assay for early syphilis were 83.3% and 92.9%; the positive and negative predictive values were 96.8% and 68.4%; and the positive and negative likelihood ratios were 11.7 and 0.2. Two specimens from patients who had suspected clinical signs were positive for amplifications of polA gene, but negative for both DFM and serological tests. We speculated they were in the very early stage of the disease.

We agree with Gayet-Ageron and colleagues1 that PCR can be used as a complementary tool for diagnosis of early syphilis, especially for those without serological conversion and visible skin lesions, in settings with a high prevalence of syphilis. However, the limitations in scaling-up of this facility-dependent technology may be a concern, especially in those resource-limited areas with an epidemic of syphilis infection.


The authors would like to thank the study site and participants for their wonderful cooperation.



  • Contributors XSC was the principal investigator of the study. RRP, YPY and XSC designed the research frame. RRP, WHW, HCW and JPZ were responsible for the study implementation and the laboratory detections. RRP and XSC were responsible for data analyses and manuscript preparation. All authors commented on the manuscript and concurred with the final submission.

  • Funding This work was supported by the National Institute of Allergy and Infectious Diseases, Sexually Transmitted Infections and Topical Microbicide Cooperative Research Center (5U19 AI031496-18).

  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; internally peer reviewed.