Laboratory evaluation of two point-of-care test kits for the identification of infectious syphilis.

Background: Syphilis is a sexually transmitted disease that can have atypical clinical presentations. Conventional laboratory tests to confirm the diagnosis are not rapid enough to affect clinical decision on treatment and contact tracing. Rapid point-of-care tests (POCT) can be useful for control of infectious diseases; however, no POCT for syphilis detection is currently available in Canada. The aim of this study is to evaluate two POCTs (Reveal^TM Rapid TP (Treponema pallidum) Antibody test and DPP^® Syphilis Screen and Confirm test) for detection of infectious syphilis.

Methods: One hundred serum samples with known syphilis serological status, based on treponemal and non-treponemal test results, were analysed in the laboratory with two POCTs by two independent operators in a blind fashion. Results were analysed to evaluate their ability to detect infectious syphilis.

Results: The Reveal Rapid TP Antibody POCT showed an overall sensitivity of 95.0% and a specificity of 83.3%, while the DPP Syphilis Screen and Confirm POCT showed a sensitivity of 87.5% and a specificity of 98.3%. Both POCTs gave a sensitivity of 100% on active syphilis samples with Venereal Disease Research Laboratory (VDRL) titres of greater than 1:4, but their sensitivities decreased for samples with low VDRL titres. Both POCTs gave weakly or very weakly reactive results on 11.3%-25.0% of the treponemal antibody positive samples.

Conclusion: This laboratory evaluation has shown promising results for both POCTs to detect infectious syphilis. Further evaluations in the field would be required to confirm this preliminary finding.