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Journal of Clinical Microbiology, October 2009, p. 3211-3217, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.01082-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Comparison of Nine Commercially Available Clostridium difficile Toxin Detection Assays, a Real-Time PCR Assay for C. difficile tcdB, and a Glutamate Dehydrogenase Detection Assay to Cytotoxin Testing and Cytotoxigenic Culture Methods{triangledown}

Kerrie Eastwood,1 Patrick Else,1 André Charlett,2 and Mark Wilcox1*

Microbiology Department, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom,1 Statistical Unit, Health Protection Agency, Centre for Infections, Colindale, London, United Kingdom2

Received 3 June 2009/ Returned for modification 19 July 2009/ Accepted 14 August 2009

The continuing rise in the incidence of Clostridium difficile infection is a cause for concern, with implications for patients and health care systems. Laboratory diagnosis largely relies on rapid toxin detection kits, although assays detecting alternative targets, including glutamate dehydrogenase (GDH) and toxin genes, are now available. Six hundred routine diagnostic diarrheal samples were tested prospectively using nine commercial toxin detection assays, cytotoxin assay (CYT), and cytotoxigenic culture (CYTGC) and retrospectively using a GDH detection assay and PCR for the toxin B gene. The mean sensitivity and specificity for toxin detection assays were 82.8% (range, 66.7 to 91.7%) and 95.4% (range, 90.9 to 98.8%), respectively, in comparison with CYT and 75.0% (range, 60.0 to 86.4%) and 96.1% (91.4 to 99.4%), respectively, in comparison with CYTGC. The sensitivity and specificity of the GDH assay were 90.1% and 92.9%, respectively, compared to CYT and 87.6% and 94.3%, respectively, compared to CYTGC. The PCR assay had the highest sensitivity of all the tests in comparison with CYT (92.2%) and CYTGC (88.5%), and the specificities of the PCR assay were 94.0% and 95.4% compared to CYT and CYTGC, respectively. All kits had low positive predictive values (range, 48.6 to 86.8%) compared with CYT, assuming a positive sample prevalence of 10% (representing the hospital setting), which compromises the clinical utility of single tests for the laboratory diagnosis of C. difficile infection. The optimum rapid single test was PCR for toxin B gene, as this had the highest negative predictive value. Diagnostic algorithms that optimize test combinations for the laboratory diagnosis of C. difficile infection need to be defined.

* Corresponding author. Mailing address: Microbiology Department, Old Medical School, Leeds General Infirmary, Leeds LS1 3EX, W. Yorks., United Kingdom. Phone: 44 113 392 6818. Fax: 44 113 343 5649. E-mail: mark.wilcox{at}leedsth.nhs.uk

{triangledown} Published ahead of print on 26 August 2009.

Journal of Clinical Microbiology, October 2009, p. 3211-3217, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.01082-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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