Clostridioides difficile PCR Tcdb Cycle Threshold predicts toxin EIA positivity but not severity of infection

Background: Diagnosis of Clostridioides difficile Infection (CDI) entails compatible clinical presentation and laboratory findings. We evaluated real-time polymerase chain reaction (qPCR) cycle threshold (C_T) as a predictor for disease severity and TcdB enzyme immunoassay (EIA) results.

Methods: Inpatients or emergency department patients who tested positive for tcdB gene by PCR were evaluated. Patients' stools underwent testing for GDH and TcdA/B by EIA. Medical health records were reviewed for demographic, clinical presentation, laboratory, treatment and outcome data. Severity of CDI was calculated using various severity score indexes.

Results: The median C_T of cases was 32.05 ± 5.45. The optimal cut-off for predicting toxin EIA positivity and severe CDI based on chart review was 32.6 and 29.8, respectively, with the area under the receiver operator characteristics curve (AUC) of 0.74 and 0.60 respectively.

Conclusion: C_T value was an acceptable predictor for EIA toxin but less so for clinical severity. Our study potentially supports a diagnostic algorithm including C_T value to reduce the number of EIA toxin assays performed.