Recently, Gayet-Ageron and colleagues published a systematic review
and meta-analysis to evaluate the diagnostic values of T. 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 a STI clinic
in Nanjing, China to evaluate the performance of PCR assay for early
syphilis diagnosis. Following ethical review by the 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 serologic testing of treponemal (TPPA) and
non treponemal (RPR) 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 old with interquartile range of 30 to 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; ?2=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; ?2=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 colleagues 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 epidemic of syphilis infection.
Funding
This work was supported by the National Institute of Allergy and Infectious Diseases, Sexually Transmitted Infections and Topical Microbicide Cooperative Research Center (5U19AI031496-18).
Reference
1. Gayet-Ageron A, Lautenschlager S, Ninet B, et al. Sensitivity,
specificity and likelihood ratios of PCR in the diagnosis of syphilis: a
systematic review and meta-analysis. Sex Transm Infect. Published Online
First: 28 Sept 2012, doi:10.1136/sextrans-2012-050622.
2. Liu H, Rodes B, Chen CY, et al. New tests for syphilis: rational
design of a PCR method for detection of Treponema pallidum in clinical
specimens using unique regions of the DNA polymerase I gene. J Clin
Microbiol. 2001;39:1941-6.
3. Centers for Disease Control and Prevention. STD Surveillance Case
Definitions. http://www.cdc.gov/std/stats10/CaseDefinitions2010.pdf.
Conflict of Interest:
None declared
Recently, Gayet-Ageron and colleagues published a systematic review and meta-analysis to evaluate the diagnostic values of T. 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 a STI clinic in Nanjing, China to evaluate the performance of PCR assay for early syphilis diagnosis. Following ethical review by the 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 serologic testing of treponemal (TPPA) and non treponemal (RPR) 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 old with interquartile range of 30 to 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; ?2=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; ?2=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 colleagues 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 epidemic of syphilis infection. Funding This work was supported by the National Institute of Allergy and Infectious Diseases, Sexually Transmitted Infections and Topical Microbicide Cooperative Research Center (5U19AI031496-18).
Reference
1. Gayet-Ageron A, Lautenschlager S, Ninet B, et al. Sensitivity, specificity and likelihood ratios of PCR in the diagnosis of syphilis: a systematic review and meta-analysis. Sex Transm Infect. Published Online First: 28 Sept 2012, doi:10.1136/sextrans-2012-050622.
2. Liu H, Rodes B, Chen CY, et al. New tests for syphilis: rational design of a PCR method for detection of Treponema pallidum in clinical specimens using unique regions of the DNA polymerase I gene. J Clin Microbiol. 2001;39:1941-6.
3. Centers for Disease Control and Prevention. STD Surveillance Case Definitions. http://www.cdc.gov/std/stats10/CaseDefinitions2010.pdf.
Conflict of Interest:
None declared