Objectives: To investigate the contribution of a real-time PCR assay for the detection of Treponema pallidum in various biological specimens with the secondary objective of comparing its value according to HIV status.
Methods: Prospective cohort of incident syphilis cases from three Swiss hospitals (Geneva and Bern University Hospitals, Outpatient Clinic for Dermatology of Triemli, Zurich) diagnosed between January 2006 and September 2008. A case–control study was nested into the cohort. Biological specimens (blood, lesion swab or urine) were taken at diagnosis (as clinical information) and analysed by real-time PCR using the T pallidum 47 kDa gene.
Results: 126 specimens were collected from 74 patients with primary (n = 26), secondary (n = 40) and latent (n = 8) syphilis. Among primary syphilis, sensitivity was 80% in lesion swabs, 28% in whole blood, 55% in serum and 29% in urine, whereas among secondary syphilis, it was 20%, 36%, 47% and 44%, respectively. Among secondary syphilis, plasma and cerebrospinal fluid were also tested and provided a sensitivity of 100% and 50%, respectively. The global sensitivity of T pallidum by PCR (irrespective of the compartment tested) was 65% during primary, 53% during secondary and null during latent syphilis. No difference regarding serology or PCR results was observed among HIV-infected patients. Specificity was 100%.
Conclusions: Syphilis PCR provides better sensitivity in lesion swabs from primary syphilis and displays only moderate sensitivity in blood from primary and secondary syphilis. HIV status did not modify the internal validity of PCR for the diagnosis of primary or secondary syphilis.
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Funding: This study was performed in the framework of the Swiss HIV Cohort Study; it was supported by the Swiss National Science Foundation and by a private donation from the “Fonds Benoit”.
Competing interests: None.
Ethics approval: This study received approval from the institutional review boards of the Bern, Geneva and Zurich University Hospitals, Switzerland.
Patient consent: Obtained.
Contributors: AG-A designed the protocol of the study together with BH, BN and LT-T. AG-A was also responsible for the organisation and the follow-up of patients, she collected data, did the statistical analysis of the study and wrote the initial draft of the manuscript. All co-authors participated in the writing of the manuscript. BN was in charge of the technical aspect of the study, validated the technique of T pallidum PCR at the Central Laboratory of Bacteriology in Geneva, and was responsible for the conduct and interpretation of all PCR assays. LT-T and VP were responsible for the recruitment of patients at the dermatology unit of Geneva’s University Hospitals. SL was in charge of the recruitment of patients at the outpatient clinic for dermatology and venereology, Triemli Hospital, Zurich. HJF was in charge of the recruitment of patients at Bern University Hospital.