The predictive value of quantitative nucleic acid amplification detection of Clostridium difficile toxin gene for faecal sample toxin status and patient outcome

Abstract

BackgroundLaboratory diagnosis of Clostridium difficile infection (CDI) remains unsettled, despite updated guidelines. We investigated the potential utility of quantitative data from a nucleic acid amplification test (NAAT) for C. difficile toxin gene (tg) for patient management.MethodsUsing data from the largest ever C. difficile diagnostic study (8853 diarrhoeal samples from 7335 patients), we determined the predicative value of C. difficile tgNAAT (Cepheid Xpert C.diff) low cycle threshold (CT) value for patient toxin positive status, CDI severity, mortality and CDI recurrence. Reference methods for CDI diagnosis were cytotoxicity assay (CTA) and cytotoxigenic culture (CTC).ResultsOf 1281 tgNAAT positive faecal samples, 713 and 917 were CTA and CTC positive, respectively. The median tgNAAT CT for patients who died was 25.5 vs 27.5 for survivors (p = 0.021); for toxin-positivity was 24.9 vs 31.6 for toxin-negative samples (p<0.001) and for patients with a recurrence episode was 25.6 vs 27.3 for those who did not have a recurrent episode (p = 0.111). Following optimal cut-off determination, low CT was defined as ≤25 and was significantly associated with a toxin-positive result (P<0.001, positive predictive value 83.9%), presence of PCR-ribotype 027 (P = 0.025), and mortality (P = 0.032). Recurrence was not associated with low CT (p 0.111).ConclusionsLow tgNAAT CT could indicate CTA positive patients, have more severe infection, increased risk of mortality and possibly recurrence. Although, the limited specificity of tgNAAT means it cannot be used as a standalone test, it could augment a more timely diagnosis, and optimise management of these at-risk patients.

Dual Reporting of Clostridioides difficile PCR and Predicted Toxin Result Based on PCR Cycle Threshold Reduces Treatment of Toxin-Negative Patients without Increases in Adverse Outcomes

“…As the majority of laboratories in North America use NAATs to diagnose CDI (26), our findings, along with other studies showing an association between lower C T and disease severity with poor outcomes (22,23,(27)(28)(29)(30), indicate dual reporting of qualitative PCR result along with CT-toxin could be implemented to identify patients who are at higher risk for CDI-related complications and most likely to benefit from CDI treatment while maintaining the high sensitivity (relative to EIA and CCNA) and rapid turnaround time of the qualitative PCR test. This testing algorithm has already shown similar efficacy in a pediatric context (31).…”

Ultrasensitive Detection of Clostridium difficile Toxins Reveals Suboptimal Accuracy of Toxin Gene Cycle Thresholds for Toxin Predictions

“…There were associations between both tcdB C T value and mortality and various signs of disease severity, and values were lower in patients who died than in survivors. The conclusions from the study were that due to the relatively low sensitivity and specificity for the confirmation of detection of toxin, tcdB C T values cannot be used as a standalone test (22).…”

High Agreement Between an Ultrasensitive Clostridioides difficile Toxin Assay and a C. difficile Laboratory Algorithm Utilizing GDH-and-Toxin Enzyme Immunoassays and Cytotoxin Testing

“…Two patients with the highest CCNA titers, 1:1,000 and 1:10,000, appeared to have CDI and responded to therapy. Of note, their NAAT cycle threshold (C T ) values were higher than the cutoff of 27, which has been reported to correlate with the presence of free toxins (15)(16)(17). Of the other 12 patients with CCNA-positive results of 1:10 or 1:100, 3 had no diarrhea in the hospital.…”