Evaluation of the Fully Automated BD MAX Cdiff and Xpert C. difficile Assays for Direct Detection of Clostridium difficile in Stool Specimens

Abstract

We evaluated the fully automated molecular BD MAX Cdiff assay (BD Diagnostics) and the Xpert C. difficile test (Cepheid) for rapid detection of Clostridium difficile infection. Culture was done on chromogenic agar followed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identification and toxin detection. Repeat testing was required for 1.8% and 6.0% of the BD MAX and Xpert tests, respectively. Sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) were 90.5%, 97.9%, 89.3%, and 98.1%, respectively, for BD MAX and 97.3%, 97.9%, 90.0%, and 99.5%, respectively, for Xpert. Clostridium difficile is the most important cause of hospitalacquired diarrhea. To implement timely infection control measures and appropriate treatment, rapid identification of toxigenic C. difficile is necessary (1). However, laboratory diagnostics remain challenging, as rapid test procedures relying on enzyme immunoassays (EIAs) show limited sensitivity (2), whereas the more-sensitive toxigenic culture and cytotoxicity assays are demanding and time-consuming. Two-step algorithms consisting of sensitive detection of glutamate dehydrogenase followed by a confirmatory toxin test have been proposed (2-4), yet the actual sensitivity has been questioned (5). Nucleic acid amplification techniques have been developed to combine low turnaround times with high sensitivity (6), but these assays require specific infrastructure. More recently, fully automated PCR assays that combine nucleic acid extraction, amplification, and detection have been developed. The Xpert C. difficile assay (Cepheid, Sunnyvale, CA) has high sensitivity and specificity and allows for accurate and rapid detection of Clostridium difficile infection (CDI). Recently, the BD MAX platform (BD Diagnostics, Franklin Lakes, NJ) has been made available; this allows for processing up to 24 samples in a fully automated PCR system. Clinical evaluation of the BD MAX Cdiff assay, based on detection of tcdB, has been published only for comparison with the BD GeneOhm assay (7).This study was conducted between April and July 2012 at the 2,000-bed tertiary care University Hospital Heidelberg. From 333 individual patients, 448 stool specimens, mostly (94.9%) soft or liquid, were examined. Samples were analyzed upon delivery or after overnight storage at 4°C. Specimens were analyzed by the BD MAX Cdiff assay and the Xpert C. difficile test. The standard technique used by the microbiology laboratory as the routine assay was the toxin A/B EIA (miniVIDAS; bioMérieux, Marcy l'Etoile, France). For the BD MAX Cdiff assay, stool samples were vortexed for 15 s and a 10-l loop was used to inoculate the sample tube. The Xpert C. difficile test and the miniVIDAS assay were done strictly in accordance with the manufacturers' protocols. As the reference method (8), stool samples were streaked onto chromID C. difficile agar plates (bioMérieux), incubated anaerobically at 35°C, and read after 24 and 48 h (9, 10). Suspicious col...

Evaluation of 3 automated real-time PCR (Xpert C. difficile assay, BD MAX Cdiff, and IMDx C. difficile for Abbott m2000 assay) for detecting Clostridium difficile toxin gene compared to toxigenic culture in stool specimens

“…Xpert showed slightly higher sensitivity than MAX (82.8% versus 81.6%), which is in line with previous studies (Dalpke et al, 2013;Viala et al, 2012) in that the sensitivity of Xpert was slightly higher than MAX (97.3% versus 90.5% and 97.8% versus 95.5%), but the sensitivities were much lower for both assays in our study. Looking into the sensitivity according to the semiquantitative growth on CDIF, the sensitivity of the Xpert, MAX, and IMDx was 97.4%, 100%, and 92.3%, respectively, for 39 samples, which showed moderate or heavy growth.…”

“…Nowadays, many rapid PCR methods to detect the toxin A and/or toxin B have been developed, which gives sensitivities and specificities that are comparable to those of toxigenic culture (Dalpke et al, 2013;Deak et al, 2014;Gilbreath et al, 2014;Stellrecht et al, 2014). Also, the continuously expanding market of Food and Drug Administration (FDA)-cleared nucleic acid amplification tests (NAATs) reflects the need for rapid and accurate diagnostic tests for CDI.…”

Comparison of GenomEra C. difficile and Xpert C. difficile as Confirmatory Tests in a Multistep Algorithm for Diagnosis of Clostridium difficile Infection

“…Diff Quik Chek Complete (QC) (TechLab, Blacksburg, VA, USA) detects by immunochromatography both GDH and toxins A and B as a single procedure device (4). The real-time PCR assay Xpert C. difficile assay (Xpert) (GeneXpert; Cepheid, Sunnyvale, CA, USA) that detects the toxin B gene (tcdB), binary toxin genes, and tcdC 117-nucleotide (nt) deletion (epidemic 027 ribotype) is frequently used as a confirmatory test because of its speed and good internal validity values (7)(8)(9)(10)(11).…”

Clostridium difficile Infection Diagnosis by Biological Molecular Methods

“…For this short presentation, we have chosen the latest references that offered the most eloquent data regarding sensitivity, specificity, and, if available, positive predictive value and negative predictive value ( Table 3) [101][102][103][104][105][106][107][108][109][110][111].…”