Evaluating the Role of Polymerase Chain Reaction (PCR) Testing for the Diagnosis of Primary Syphilis: A Population-Cohort Study

Background. There are syphilis outbreaks throughout North America, despite previous hopes of eradication. Serologic testing for syphilis requires multiple serologic tests which can yield varying interpretations. PCR testing has been implemented in many centres for use in epidemic settings such that public health departments can follow-up on cases that may initially be serologically negative. Smaller studies of PCR testing have demonstrated high levels of accuracy. We aim to assess the utility and characteristics of PCR testing in primary syphilis diagnosis in a large Canadian healthcare region. Methods. A cohort study from 2007 through 2013 was conducted using a provincial database of syphilis testing in adults. Patients with genital lesions who underwent PCR and serology testing (within −7 to +28 days of PCR testing) at two regional specialized sexually transmitted infection clinics were included. The primary outcome was the proportion of PCR positivity. Test characteristics were compared between multiple serologic tests to PCR testing. Herpes simplex virus (HSV) PCR testing was also performed due to similarity of lesion appearance. Sensitivity and specificity were calculated as the percent of results PCR positive divided by serology positive and PCR negative divided by serology negative, respectively. Results. A total of 3600 patients aged ≥18 years with genital lesions (clinically suspected to be syphilis) had PCR and serology testing performed. Of these, 114 (3.0%) were PCR positive. There were 14 patients who were PCR positive but had negative serology. Excluding those positive for HSV (1532; 43%), a total of 109 cases of primary syphilis occurred in the study period. 105 positive by PCR and 94 positive by serology. Our calculated sensitivity and specificity of 95.7% and 99.3%, respectively, are consistent with previously published data. Using a 2014 provincial estimated incidence of 3.3 cases/100,000, negative predicted value of syphilis PCR testing was 99.9% and similar to published values. Conclusion. In our large cohort study spanning seven years, PCR was highly sensitive and specific, with an excellent NPV in the diagnosis of primary syphilis. We recommend PCR testing as an adjunct to serology to aid in syphilis diagnosis in an outbreak setting. Disclosures. All authors: No reported disclosures

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