The Sensitivity of PCR combined with the Specificity of Toxin Enzyme Immunoassay: Could an Ultra-sensitive Single Molecule Counting Technology Offer a Standalone Solution for Diagnosis of Clostridioides difficile Infection?

Abstract

Background Clostridioides difficile infection (CDI) continues to cause significant morbidity and avoidable mortality worldwide. Results from an ultra-sensitive toxin immunoassay (Singlulex Clarity C. diff toxins A/B assay) were compared with those of various other diagnostic and reference methods/algorithms for the detection of C. difficile. Methods 293 residual clinical stool samples were tested using the Singulex assay. In total, 188 samples were tested by GDH and 239 were tested by PCR. All toxin B PCR (Serosep EntericBio C. difficile assay) positive samples (n=168) and prospectively tested GDH samples (n=97) were also tested using membrane-type toxin EIA (MT-EIA; Techlab Tox A/B Quik Chekò). Culture (alcohol shock and Brazier’s media; Oxoid) and ribotyping (capillary electrophoresis using Bidet et al. primers) information was available for 205 samples. Results The positive percent agreement (PPA) and negative percent agreement (NPA) of the Singulex Clarity C. diff toxins A/B assay compared with: GDH; toxin EIA; PCR; GDH/toxin EIA; GDH/toxin EIA/PCR; PCR/toxin EIA and culture were – 61% & 92%; 97% & 50%; 69% & 90%; 100% & 51%; 81% & 77%; 96% & 65%; and 69% AND 52% respectively. Conclusions The Singulex Clarity C. diff toxins A/B assay had high PPA compared to toxin EIA and multistep algorithms ending with toxin EIA, and high NPA compared to PCR and a multistep algorithm ending with PCR. The Singulex Clarity assay has the potential to be used as a standalone test for CDI diagnosis; additional clinical studies are required and will soon be underway.