Diagnostic relevance of polymerase chain reaction technology for T. pallidum in subjects with syphilis in different phases of infection.

Although serology is a valid tool for the clinician to manage syphilis infection, there are still some cases in which evidence of the presence of T. pallidum or its specific components, such as specific DNA segments, may be useful to establish or confirm the diagnosis. In the absence of T. pallidum grown in culture, a nested PCR to amplify a specific segment of the microorganism genome was performed in ulcerative secretions or sera, after DNA extraction, using a commercially available kit. A kit validation was based on the observation of no positivities in patients without ongoing or anamnestic infection (40 patients). On the contrary, patients infected with T. pallidum presented positivities both in ulcerative secretions and in sera with frequencies that depended on the disease phase and type of sample. In fact, even after treatment, ulcerative secretions that were negative in dark-field examination were found to be positive in PCR. In addition, the sera of patients with positive specific IGM (serologically diagnosed syphilis, asymptomatic state) were also positive in PCR. This test could, therefore, be useful to analyze difficult situations, especially when a seropositivity for a previous infection may complicate the serology of a reinfection or when therapies interfere with dark-field microscopic observation.