Molecular Methods Detect Common Cause of Diarrhea

Molecular based tests detect up to 50% more cases of Clostridium difficile than other conventional immunoassays.

Although the molecular technology is more expensive, it allows for more cases to be identified and assists in patient safety efforts within the hospital in terms of preventing hospital-acquired C. difficile infections.

Scientists at Rhode Island Hospital (Providence, RI, USA) compared five different assays used in the laboratory for identifying C. difficile and evaluated the results of molecular versus nonmolecular tests. Consecutive liquid or soft stool specimens were obtained from hospitalized patients and transported refrigerated to the network laboratory for detection of C. difficile toxin from July 28, 2009, to August 28, 2009. Of 89 patients who submitted specimens, 81 patients had symptoms compatible with C. difficile infection (CDI), were included in the study.

A membrane-bound lateral-flow immunoassay was used to screen stool specimens for the presence of C. difficile GDH-specific antigens. Samples, positive using the C. Diff Quik Check test (TechLab, Inc.; Blacksburg, VA, USA), underwent reflex testing using the Premier Toxin A and B Enzyme Immunoassay (Meridian Bioscience, Inc.; Cincinnati, OH, USA) to confirm the presence of C. difficile toxins A and B. The three molecular detection assays were the BD GeneOhm Cdiff Assay (Becton, Dickinson and Co.; Franklin Lakes, NJ, USA); the Xpert C. difficile test (Cepheid; Sunnyvale, CA, USA); and the ProGastro Cd Assay (Prodesse; Inc.; Waukesha, WI, USA).

The molecular methods detected 35% to 54% more specimens positive for C. difficile compared with nonmolecular methods. The better performance of molecular versus nonmolecular methods was significant for all methods evaluated. The BD GeneOhm Cdiff assay was the most efficient at 96.2%, followed by the Xpert C. difficile test at 92.5%, and the ProGastro Cd assay at 88.5%. The nonmolecular C. Diff Quik Chek Complete test had an efficiency score of 61.5%. The new molecular test, the BD GeneOhm Cdiff assay was more cost-effective than a previously used method. The costly the Xpert C. difficile test required limited processing and yielded rapid results, while because of discordant results, specimen processing, and extraction equipment requirements, the ProGastro Cd assay was the least favored molecular assay.

Kimberle Chapin, MD, director of the network laboratory, said, "Through the use of molecular testing in our laboratory, combined with astute physicians and nurses requesting the tests, we were able to detect 50% more patients than we did prior to using molecular methods. Knowing the nonmolecular tests did not find as many cases lead to patient safety concerns and the drive to implement the new method." The study was published on July 4, 2011, in the Journal of Molecular Diagnostics.

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Rhode Island Hospital
TechLab
Meridian Bioscience