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Evaluation of Copan FecalSwab as Specimen Type for Use in Xpert C. difficile Assay
Michael J Mashock1, Matthew L Faron1, Blake W Buchan1,2
1Medical College of Wisconsin, Milwaukee, Wisconsin, U.S.A. America.
Abstract:
Liquid-based microbiology (LBM) devices incorporating flocked swabs and preservation medium ease transport of specimens and improve specimen yield compared to traditional fiber wound swabs; however, the performance of LBM collection devices has not been evaluated in many molecular assays. It is unclear how the differences in matrix and specimen loading with an LBM device will affect test performance compared to traditional collection devices. The purpose of this study was to evaluate the performance of specimens collected in FecalSwab transport medium (Copan Diagnostics, Murrieta, CA) compared to unpreserved stool using the Cepheid Xpert C. difficile assay (Cepheid, Sunnyvale, CA). Results equivalent to unpreserved stool samples were obtained when 400 μl of FecalSwab-preserved stool was employed in the Xpert assay. The positive and negative percent agreement of specimens inoculated with FecalSwab medium (n = 281) was 97.0% (95% confidence interval [CI], 90.9 to 96.4%) and 99.4% (95% CI, 96.4 to 99.9%), respectively, compared to reference results obtained using unpreserved stool. Throughout this study, only four discrepant results occurred when comparing preserved specimens to unpreserved stool specimens in the Xpert C. difficile PCR assay. Post discrepant analysis, using the BD MAX Cdiff assay, the specificity and sensitivity both increased to 100%. The high positive and negative percent agreements observed in this study suggest that stool preserved in FecalSwab media yields equivalent results to using unpreserved stool when tested on the Xpert C. difficile assay, allowing laboratories to adopt this liquid-based microbiology collection device.
Insights
Liquid-based microbiology devices using FecalSwab transport medium provide results equivalent to unpreserved stool for *Clostridioides difficile* testing. This validates their use in molecular assays, improving laboratory diagnostics.
Area of Science:
- Clinical Microbiology
- Molecular Diagnostics
- Infectious Disease Detection
Background:
- Liquid-based microbiology (LBM) devices offer advantages in specimen transport and yield over traditional swabs.
- The impact of LBM matrices on molecular assay performance, specifically for *Clostridioides difficile* (*C. difficile*), requires further evaluation.
- Understanding matrix effects is crucial for adopting new collection devices in diagnostic laboratories.
Purpose of the Study:
- To evaluate the performance of the Cepheid Xpert *C. difficile* assay using stool specimens collected in FecalSwab transport medium.
- To compare the diagnostic accuracy of LBM-preserved specimens against unpreserved stool samples.
Main Methods:
- Specimens were collected using FecalSwab transport medium and tested with the Cepheid Xpert *C. difficile* assay.
- Results were compared to those obtained from unpreserved stool samples analyzed with the same assay.
- Discrepant results were further analyzed using the BD MAX Cdiff assay.
Main Results:
- Equivalent results were achieved when using 400 μl of FecalSwab-preserved stool in the Xpert assay.
- High positive (97.0%) and negative (99.4%) percent agreement were observed between preserved and unpreserved specimens.
- Post-discrepant analysis with the BD MAX Cdiff assay demonstrated 100% sensitivity and specificity.
Conclusions:
- Stool specimens preserved in FecalSwab transport medium yield equivalent results to unpreserved stool for *C. difficile* detection via the Xpert assay.
- LBM collection devices are suitable for use in *C. difficile* molecular testing, facilitating laboratory adoption.
- This study supports the integration of LBM devices into routine molecular diagnostic workflows.
