(P100) A COMBINED TREPONEMAL/NONTREPONEMAL ASSAY FOR POINT-OF-CARE SYPHILIS TESTING

Background:
Syphilis is one of the fastest growing sexually transmitted infections (STI) in the United States. The current diagnostic method requires a confirmatory test following an initial positive result. This leads to long turnaround times and higher chances of loss to follow-up, ultimately increasing the risk of continued spread. Here we present progress towards a combined treponemal/nontreponemal quantitative syphilis antibody detection assay for use on a point-of-care diagnostic platform.

Methods:
We developed a magnetic bead-based proximity extension assay (PEA) to detect treponemal antibodies. Treponemal antibodies were captured using antigen-coated magnetic beads, tagged with DNA probes, and amplified with PCR. Ct values of qPCR results and R2 values of standard curves were determined in the QuantStudio Design and Analysis software and Excel, respectively. In conjunction with the assay, a rapid diagnostics platform to automate sample processing and PCR has been developed.

Results:
We have demonstrated sensitivity of 0.7 ng/mL, demonstrating nearly two orders of magnitude higher sensitivity than the gold standard TPPA assay (~56 ng/mL). We have also demonstrated the quantitative ability of the assay with a linear standard curve R2-value of 0.92. The portable diagnostic platform performs automated sample processing via magnetic bead transfer through different buffers in under 10 minutes. Within the same run, the instrument’s rapid thermocycling can achieve 50 cycles of PCR in under 20 minutes.

Conclusion:
We have demonstrated a proof-of-concept for a quantitative PCR-based immunoassay for the detection of treponemal antibodies. Further development with a nontreponemal antibody detection assay combined with our rapid diagnostic platform can streamline syphilis diagnosis by providing both treponemal and nontreponemal titer results within a single patient visit.