Evaluation of Copan FecalSwab as Specimen Type for Use in Xpert C. difficile Assay

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.

Direct detection and characterization of Clostridium difficile from a novel collection device to improve laboratory workflow

“…Since this study was carried out during a real laboratory diagnostic routine, the bacterial load of samples was variable and standardization of inoculum in the FecalSwab TM was not possible. However, we successfully used 1 mL of transport medium as template for Xpert C. difficile BT, obtaining a median Ct value for tcdB of 27.5 (range 21.7-36.5), comparable to the values observed when unpreserved specimens are used as templates (16).…”

“…In this study, results obtained using the FecalSwab™ medium as template for the Xpert C. difficile BT were comparable with those obtained by toxigenic culture (TC), supporting the FecalSwab™ as a suitable template for this molecular assay. A recent study, evaluating the performance of FecalSwab™ as specimen type for the Xpert C. difficile BT, indicated 1.5 × 10 4 CFU/mL in 400 μL of preservation medium as the optimal template . Since this study was carried out during a real laboratory diagnostic routine, the bacterial load of samples was variable and standardization of inoculum in the FecalSwab™ was not possible.…”

“…In this study, results obtained using the FecalSwab TM medium as template for the Xpert C. difficile BT were comparable with those obtained by toxigenic culture (TC), supporting the FecalSwab TM as a suitable template for this molecular assay. A recent study, evaluating the performance of FecalSwab TM as specimen type for the Xpert C. difficile BT, indicated 1.5 9 10 4 CFU/mL in 400 lL of preservation medium as the optimal template (16).…”

Evaluation of the FecalSwab for Stool Specimen Storage and Molecular Detection of Enteropathogens on the BD Max System

“…Baseline mean C T values for the majority of enteropathogens ranged from 24 to 27 with the exception of Salmonella ( C T = 30.1), rotavirus ( C T = 10.9), astrovirus ( C T = 15.5), and adenovirus ( C T = 9.2). We considered a change in C T (Δ C T ) score from baseline (day 0) to be equivalent if ≤1 ( 6 ) and a Δ C T of ≥1.1 to be a loss or less than or equal to a −1.1 gain in detection ( Fig. 3 ).…”

Clinical evaluation of a non-purified direct molecular assay for the detection of Clostridioides difficile toxin genes in stool specimens

“…C. difficile strain ATCC9689 was spiked into negative pooled stool samples at a concentration of 1.5 × 10 7 CFU/mL, 1.5 × 10 6 CFU/mL, 1.5 × 10 5 CFU/mL, 7.5 × 10 4 CFU/ mL, 5.0 × 10 4 CFU/mL, 3.0 × 10 4 CFU/mL, 1.5 × 10 4 CFU/mL, and 1.5 × 10 3 CFU/mL for each set of two pooled stool samples and one demineralized water sample. For the concentration, 1 McFarland was regarded as approximately 3.0 × 10 7 CFU/mL as previously described [25]. For the GENECUBE C. difficile assay, 50 μL spiked sample was used for assay evaluation and tests were performed four times for each sample.…”