Alice S. Weissfeld

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

ABSTRACT 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 Fishers 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.

FDA Regulation of Clinical Microbiology Diagnostic Devices

The Food and Drug Administration (FDA) is charged with protecting the public health by ensuring the safety and efficacy of human and veterinary drugs, biological products, and medical devices. It is also charged with ensuring the safety of foods, cosmetics, and radiation-emitting products. More

Straight from the Headlines: What Is Going On in Compounding Pharmacies, and How Can Clinical Microbiologists Help?

In late 2004, I was the outgoing Chair of the American Society for Microbiologys (ASMs) Committee on Professional Affairs in Microbiology. The U.S. Pharmacopeial Convention sent a letter to ASM asking us to comment on their newly minted chapter , regarding compounded sterile preparations (

Designing Studies Acceptable for Abstraction and Inclusion in Evidence-Based Laboratory Practice Guidelines.

Expansion of technologies, changing infrastructure, and dwindling resources have produced the need for health care reform and changes in clinical laboratories. The health care model will have to shift increasingly from a fee-for-service model to a value-based model. ABSTRACT Expansion of technologies, changing infrastructure, and dwindling resources have produced the need for health care reform and changes in clinical laboratories. The health care model will have to shift increasingly from a fee-for-service model to a value-based model. Laboratories will have to focus more on evidence-based outcome studies evaluating the effects of their preanalytical and postanalytical practices on real patient outcomes. Although well-designed clinical trials and multicenter studies are needed to determine the effects of laboratory processes on outcomes, there has been concern that too few well-designed studies have been published. To help improve the quality of study design and to facilitate reporting transparency, several method statements have been developed. The Standards for Reporting of Diagnostic Accuracy Studies (STARD) initiative was recently updated, listing 30 items deemed crucial for transparent reporting of studies, thereby allowing the creation of a robust database for clinical practice guidelines. Three methods describing the assessment of the quality of data on which to base recommendations for such guidelines are also available. Close attention must be given to study design so that parameters ensuring study quality are met, thereby allowing inclusion of the study data in the formulation of evidence-based laboratory best practices guidelines.