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Evaluation of the Xpert Clostridioides difficile BT Assay using FecalSwab stool samples
Simon Michaelis1, Julia Stocker1, Christopher Schneider1
1Institute of Clinical Chemistry and Laboratory Medicine, General Hospital Hochsteiermark, Vordernberger Straße 42, 8700 Leoben, Austria.
Objectives:
The molecular detection of toxigenic Clostridioides difficile (C. difficile) infections mostly relies on the use of unpreserved stool specimens. However, recently the feasibility of sampling systems for stool pathogen detection comprising flocked swabs and preservation media has been highlighted. Hence, we evaluated the Copan FecalSwab stool sampling systems for the detection of toxigenic C. difficile by the Cepheid Xpert C. difficile BT PCR assay.
Methods:
Unpreserved stool samples from patients with suspected toxigenic C. difficile infections were tested for C. difficile using the Xpert C. diff BT PCR assay on a Cepheid GeneXpert IV device (Cepheid, Sunnyvale, CA, USA). In parallel, from this stool sample a flocked swab sample was taken and transferred into a FecalSwab preservation tube. Subsequently, 400 µL of the preservation media was utilized for performing the Xpert C. difficile BT PCR. From the same FecalSwab sample an immunological rapid test for the detection of C. difficile (C. DIFF QUIK CHEK COMPLETE, Techlab, Blacksburg, VA, USA) was performed, representing the current analytical standard in our hospital. The qualitative results of all tests and the cycle threshold (Ct) values from the PCR runs were compared.
Results:
Fortytwo unpreserved stool samples were included, of whom 16 were positive for toxigenic C. difficile. Fifteen were also detected positive using the FecalSwabs. Hence, the qualitative agreement was almost perfect (Cohen's kappa 0.949, p < 0.001). The Ct values compared between the sampling materials correlated well (Spearman's Rho 0.893, p < 0.001). However, in comparison the median Ct value obtained from the unpreserved stool samples was lower (23.6 versus 25.6). A median Ct value difference of 1.3 was observed.
Conclusions:
The FecalSwab is suitable for preanalytical stool collection for the detection of toxigenic C. difficile with the Xpert C. difficile PCR test. However, to reach optimal sensitivity the preanalytical processing may need further investigations.
