Evaluation of a New Automated Homogeneous PCR Assay, GenomEra C. difficile, for Rapid Detection of Toxigenic Clostridium difficile in Fecal Specimens

Abstract

bWe evaluated a new automated homogeneous PCR assay to detect toxigenic Clostridium difficile, the GenomEra C. difficile assay (Abacus Diagnostica, Finland), with 310 diarrheal stool specimens and with a collection of 33 known clostridial and nonclostridial isolates. Results were compared with toxigenic culture results, with discrepancies being resolved by the GeneXpert C. difficile PCR assay (Cepheid). Among the 80 toxigenic culture-positive or GeneXpert C. difficile assay-positive fecal specimens, 79 were also positive with the GenomEra C. difficile assay. Additionally, one specimen was positive with the GenomEra assay but negative with the confirmatory methods. Thus, the sensitivity and specificity were 98.8% and 99.6%, respectively. With the culture collection, no false-positive or -negative results were observed. The analytical sensitivity of the GenomEra C. difficile assay was approximately 5 CFU per PCR test. The short hands-on (<5 min for 1 to 4 samples) and total turnaround (<1 h) times, together with the high positive and negative predictive values (98.8% and 99.6%, respectively), make the GenomEra C. difficile assay an excellent option for toxigenic C. difficile detection in fecal specimens.T oxin-producing Clostridium difficile is the most common cause of hospital-acquired and antibiotic-associated diarrhea (1, 2). The main virulence factors of C. difficile are C. difficile toxin A (TcdA) and C. difficile toxin B (TcdB), which are encoded by the genes tcdA and tcdB, respectively (3, 4). In addition, a separate binary toxin is produced by a small group of isolates with or without TcdA and/or TcdB (5, 6), and it has been suggested that the binary toxin may play a part in the recurrence of C. difficile infection (CDI) (7). As the role of the binary toxin in CDI currently is not well understood, it has not become a common target for diagnostic assays.CDI is prevalent in many hospitals and health care facilities throughout the world. It is associated with increases in hospitalization times and mortality rates, leading to augmented health care costs (2,6,8). In order to limit the transmission of C. difficile and to decrease the burden of CDI, rapid reliable detection of toxigenic C. difficile isolates and good infection prevention practices are required.Cytotoxigenic cultures and cytotoxin assays are considered standard diagnostic methods. These are sensitive but have several drawbacks, including long turnaround times and labor-intensive sample preparation and analysis, which limit their clinical utility (9-13). An alternative approach is the detection of C. difficile toxins or glutamate dehydrogenase (GDH) in stool samples by immunochromatographic antigen (IA) tests or enzyme immunoassays (EIAs) (14-16). These assays are rapid but are less sensitive and less specific than toxigenic cultures. Moreover, relying only on GDH detection reveals nothing about the toxigenic nature of the possible C. difficile isolates. To improve the detection of CDI using IA tests or EIAs, a two-step diagnostic algorithm has bee...

Prospective Evaluation of the mariPOC Test for Detection of Clostridioides difficile Glutamate Dehydrogenase and Toxins A/B

“…The sensitivity of GenomEra PCR has been reported to be similar to those of several other nucleic acid amplification-based methods (32,33), thus being a valid molecular test for our comparison study. The specificity of the GenomEra PCR test in our study was better than what has previously been reported (32)(33)(34). The sensitivities obtained in our study from clinical specimens are also in line with the analytical sensitivities of the mariPOC (2018-02 user's manual) and TechLab (2016/07 user's manual) tests stated by the manufacturers: 0.7 ng/ml versus 0.8 ng/ml for GDH, 0.1 ng/ml versus 0.63 ng/ml for toxin A, and 0.1 ng/ml versus 0.16 ng/ml for toxin B, respectively.…”

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

“…After retesting, all except 1 gave positive results. In the only published evaluation of this assay, Hirvonen et al found only 1 borderline result from 310 specimens tested with GenomEra (0.3%) (16). After retesting, this specimen, which was positive for toxigenic culture, yielded a negative result.…”

European Society of Clinical Microbiology and Infectious Diseases: update of the diagnostic guidance document for Clostridium difficile infection

“…Eight studies (23%) used an enrichment broth before plating onto a solid agar [19,22e24,32,43,58,62]. Toxigenicity was confirmed by PCR (15/32, 47%) [21,23,29,33e35,37,51e57,70], CCNA (9/32, 28%) [7,8,22,24,43,47,58,61,62], toxin EIA (7/32, 22%) [19,30,32,38,40,69,71] or both PCR and CCNA (1/32, 3%) [26]. Blinding (index test interpreted without knowledge of reference test or vice versa) was reported in 8 (14%) of 56 studies.…”