Two commercial isothermal amplification assays have been compared for the detection of Clostridium difficile toxin in fresh fecal samples from adult and pediatric patients.

Laboratory diagnosis of C. difficile is routinely accomplished by the detection of produced toxins, detection of toxin genes, or a two-step approach where the detection of a C. difficile–specific antigen, glutamate dehydrogenase, is followed by detection of toxins or toxin genes.

Laboratory scientists at the Nationwide Children's Hospital (Columbus, OH, USA) and their colleagues collected a total of 758 fresh stool specimens, liquid or soft, submitted for C. difficile testing as part of routine patient care from January 2013 till September 2013. There were no age restrictions on the patient specimens. Inclusion criteria were an order of C. difficile testing as part of standard of care testing for patients with symptoms of diarrhea.

All stool samples were tested for the presence of C. difficile toxin gene using the Illumigene assay (Meridian Biosciences; Cincinnati, OH, USA). Fifty microliters of the treated sample was added to the reaction buffer and placed into the Meridian Biosciences’ illumipro-10 instrument where isothermal amplification and detection was performed. Remnant stool specimens from patients that were enrolled in the study were deidentified and tested by the AmpliVue assay (Quidel; San Diego, CA, USA). Any discordant results were resolved by performing toxigenic culture.

The AmpliVue C. difficile assay showed 97.8% concordance with the Illumigene assay. Among all three sites where the study was performed, there were 16 discrepant results that were resolved by performing cytotoxigenic culture in these samples. Following discordant resolution, the combined performance for all three sites for sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for AmpliVue was 96.1%, 99.2%, 96.1%, and 99.2%, respectively, while for Illumigene was 96.1%, 99.8%, 99.2%, and 99.2%, respectively.

The authors concluded that both AmpliVue and Illumigene C. difficile assays can be used in diverse laboratory settings with both adult and pediatric patient populations. They can reliably detect the presence or absence of C. difficile toxin genes in stool samples, providing fast results for the proper treatment of patients and initiation of infection control measures. The study was published in the August 2015 issue of the journal Diagnostic Microbiology and Infectious Disease.

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Nationwide Children's Hospital 
Meridian Biosciences 
Quidel