Correlation between rapid antigen test and PCR for detection of toxin genes in Clostridioides difficile : A comparative study of diagnostic performance

Sammanfattning

In healthcare settings, Clostridioides difficile-infection (CDI) is a common reason for antibiotic-associated diarrhea. Therefore, rapid and accurate diagnosis is essential for appropriate treatment and infection control. This study aimed to evaluate the diagnostic performance of the antigen and toxin-based method, TECHLAB® C. DIFF QUIK CHEK COMPLETE®, compared to the PCR-method with BD MAX™ Cdiff, for diagnostics of C.difficile. In this study, a total of 72 samples of residual faeces from a selected range of patients were included. The samples were submitted to the department of clinical microbiology, Falu Hospital for routine testing of toxigenic C. difficile. After exclusion of invalid results, 70 samples were included and analyzed. Results from the QUIK CHEK were compared against results from the BD MAX, including both BD MAX software interpretations and manual review of amplification curves, CT-values and fluorescence data. The statistical analysis was performed in R studio using a McNemar’s 𝜒2 test. In addition, routine statistics from Dalarna 2025, cost of the methods, as well as hands-on and turnaround times were analyzed. PCR-based diagnostics identified a higher number of positive samples compared to the antigen and toxin-based method (p < 0.0001). The increased proportion of PCR-positive results was mainly observed amongst samples with a QUIK CHEK-inconclusive result and could not be linked to subsequent toxin detection. Manual review resulted in reclassification in a total of four samples in borderline cases, which indicates possible presence of non-viable bacteria. The cost analysis showed a higher per-sample-cost for the PCR-method as well as noclear advantage regarding hands-on and turnaround times. In conclusion, even if PCR-based diagnostics with BD MAX identifies a larger number of positive samples than the routine analysis with QUIK CHEK, it does not identify a larger number of clinically relevant samples. The antigen and toxin-based method offers a balanced diagnostics with clinical specificity, cost effectiveness and adaptation to the laboratories workflow. This speaks for continued use of QUIK CHEK for routine diagnostics of C.difficile infections at the department of microbiology, Falu Hospital.