Clostridium difficile Testing in the Clinical Laboratory by Use of Multiple Testing Algorithms

• Published in: Journal of Clinical Microbiology Vol. 48; no. 3; pp. 889 - 893
• Main Authors: Novak-Weekley, Susan M, Marlowe, Elizabeth M, Miller, John M, Cumpio, Joven, Nomura, Jim H, Vance, Paula H, Weissfeld, Alice
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01-03-2010; American Society for Microbiology (ASM)
• Subjects: Algorithms; Animals; Bacterial Proteins - analysis; Bacterial Proteins - genetics; Bacterial Proteins - toxicity; Bacterial Toxins - analysis; Bacterial Toxins - genetics; Bacterial Toxins - toxicity; Bacteriological Techniques - methods; Bacteriology; Biological and medical sciences; Cell Culture Techniques; Cercopithecus aethiops; Clostridium difficile; Clostridium difficile - genetics; Clostridium difficile - isolation & purification; Clostridium Infections - diagnosis; Clostridium Infections - microbiology; Enterotoxins - analysis; Enterotoxins - genetics; Enterotoxins - toxicity; Feces - microbiology; Fundamental and applied biological sciences. Psychology; Glutamate Dehydrogenase - analysis; Humans; Immunoenzyme Techniques - methods; Microbiology; Miscellaneous; Neutralization Tests; Polymerase Chain Reaction - methods; Predictive Value of Tests; Sensitivity and Specificity; Vero Cells; Clostridiales; Bacteria; Algorithm; Clostridiaceae; Clostridium difficile
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.01801-09

The incidence of Clostridium difficile infection (CDI) has risen almost 3-fold in the United States over the past decade, emphasizing the need for rapid and accurate tests for CDI. The Cepheid Xpert C. difficile assay is an integrated, closed, nucleic acid amplification system that automates sample preparation and real-time PCR detection of the toxin B gene (tcdB). A total of 432 stool specimens from symptomatic patients were tested by a glutamate dehydrogenase (GDH) assay, a toxin A and B enzyme immunoassay (EIA), the Xpert C. difficile assay, and a cell culture cytotoxicity neutralization assay (CCCN). The results of these methods, used individually and in combination, were compared to those of toxigenic culture. Results for the Xpert C. difficile assay alone showed a sensitivity, specificity, positive predictive value, and negative predictive value (NPV) of 94.4, 96.3, 84.0, and 98.8%, while the EIA alone gave corresponding values of 58.3, 94.7, 68.9, and 91.9%, respectively. An algorithm using the GDH assay and the EIA (plus the CCCN if the EIA was negative) showed corresponding values of 83.1, 96.7, 83.1, and 96.1%. The Xpert C. difficile assay was statistically superior to the EIA (P, <0.001 by Fisher's exact test) and to the GDH-EIA-CCCN algorithm (P, 0.0363). Combining the GDH and Xpert C. difficile assays lowered both the sensitivity and the NPV of the Xpert assay. The GDH-EIA-CCCN procedure required, on average, 2 days to complete testing on GDH-positive results, while testing by the Xpert C. difficile assay was completed, on average, in less than 1 h. Xpert C. difficile testing yielded the highest sensitivity and NPV, in the least amount of time, of the individual- and multiple-test algorithms evaluated in this study.