Molecular testing best for C. difficile

Chapin KC. J Mol Diagn. 2011;13:395-400.

Results from a comparison study of molecular vs. non-molecular testing for Clostridium difficile toxin have shown that molecular testing detects 35% to 54% more positive specimens than other methods.

Molecular technology is more costly, but it allows more cases to be identified and assists in patient safety efforts within the hospital in terms of preventing hospital-acquired C. difficile infections (CDIs), according to Kimberle Chapin, MD, and colleagues. Chapin is director of the microbiology lab at Lifespan, a Rhode Island health system, and also holds an academic appointment at The Warren Alpert Medical School of Brown University in Providence, R.I.

The study compared five different assays used in the laboratory for identifying C. difficile at Rhode Island Hospital/Hasbro Children’s Hospital, The Miriam Hospital and Newport Hospital, where more than 15,000 C. difficile assays are used each year.

Performance parameters of five assays for detection of C. difficile toxin were compared using fresh stool samples from patients with CDI. Assays were performed simultaneously and according to manufacturer instructions. Patient inclusion was dependent on clinical presentation consistent with CDI criteria.

Specimens were considered true positive if positive by two or more assays. Eighty-one patients were evaluated, and 32.1% (26/81) of the population was positive for CDI. The increase in performance of molecular methods vs. non-molecular methods was significant (P<.03 for all methods evaluated), the researchers wrote.

Chapin said these findings bring up concerns in the number of unconfirmed cases of C. difficile in hospitals that are not using molecular methods.

“Through the use of molecular testing in our lab, 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 non-molecular tests did not find as many cases lead to patient safety concerns and the drive to implement the new method,” Chapin said in a press release about the study.

The molecular methods tested in the study included:

BD GeneOhm Cdiff assay (BD Diagnostics)
Xpert C. difficile test (Cepheid)
proGastro Cd assay (Gen-Probe Prodesse Inc.)

The non-molecular methods included in the study were:

Wampole C. Diff Quik Chek (TechLab)
Meridian Premier toxin A and B assay (Meridian Bioscience)
Wampole C. Diff Quik Chek Complete (TechLab)

Disclosure: Reagent kits for the BD GeneOhm C. difficile assay were provided by Becton, Dickinson and Co., and for the Xpert C. difficile test by Prodesse Inc.

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