P-2095. Ultrasensitive <i>Clostridioides difficile</i> Toxin A/B Assay (in Development) for Higher Diagnostic Accuracy

Abstract Background Diagnostic tests for Clostridioides difficile infection (CDI) have either poor sensitivity or specificity, which has led to guideline recommendations for complex multistep testing algorithms. Ultrasensitive C. difficile toxin A/B measurements correlate with disease and may offer a standalone solution for CDI diagnosis. Fluxus develops ultrasensitive, target-agnostic, and low-complexity single-molecule diagnostic instruments based on optofluidic technology that combines integrated optics and microfluidics on a single chip-based system. Here, we report on the preliminary analytical performance of C. difficile toxin A and B assays (in development) powered by the Fluxus technology. Methods C. difficile toxin A (TcdA) and B (TcdB) were spiked into buffer and stool (pooled) and tested across a wide range of TcdA/TcdB concentrations to give dose-response curves and estimate limits of detection (LoD; assay background +2.5 STD of background) and quantification (LoQ; assay background +10 STD of background). TcdA and TcdB concentrations were calculated from a four-parameter logistic nonlinear regression-based calibration curve. Crossreactivity between the toxins was assessed. Further evaluation of expanded analytical and clinical performance is ongoing. Results LoDs in buffer for the prototype TcdA and TcdB assays were 0.47 and 0.98 pg/mL, respectively, and LoQs were 0.91 and 3.34 pg/mL, respectively, with a high dynamic range. LoDs in spiked stool for the TcdA and TcdB assays were 2.02 and 1.15 pg/mL, respectively, and LoQs were 4.25 and 4.35 pg/mL, respectively. There was no crossreactivity between the assay targets across a 4-log dynamic range. Conclusion Fluxus’ ultrasensitive C. difficile toxin A/B assays in development can detect TcdA and TcdB at pg/mL concentrations. Preliminary evaluation of spiked stool samples indicates a comparable dilution linearity to calibrator dose response in buffer. An ultrasensitive C. difficile toxin A/B assay has the potential to provide both high clinical sensitivity and specificity and may replace current testing methods. Disclosures Gipshu Dave, MS, Fluxus, Inc.: Stocks/Bonds (Public Company) Tiffany Truong, MS, Fluxus, Inc.: Stocks/Bonds (Public Company) Mariya Soban, MS, Fluxus, Inc.: Stocks/Bonds (Public Company) Justin Nguyen, BS, Fluxus, Inc.: Stocks/Bonds (Public Company) Frank Zaugg, PhD, Fluxus, Inc.: Stocks/Bonds (Public Company) Valerie Brachet, PhD, Fluxus, Inc.: Stocks/Bonds (Public Company) Peter Wagner, PhD, Fluxus, Inc.: Stocks/Bonds (Public Company) Johanna Sandlund, MD, PhD, Fluxus, Inc.: Stocks/Bonds (Public Company)