From the Editor

Friday, December 23, 2016 Published in On-Demand Fall 2010 Written by David Persing M.D., Ph.D., Chief Medical and Technology Officer, Cepheid

Bamboozled

That’s the word that comes to mind when I think of the evolution of C. difficile diagnostic testing over the past decade. The problem has been that commercial tests have evolved in the wrong direction, and lab directors worldwide have been duped into thinking that all was copacetic all along. Indeed, recently published data confirms what treating physicians have known all along—that the toxin immunoassays run in most labs exhibit poor sensitivity and specificity for detection of C. difficile infection. New guidelines from APIC encourage laboratories to return to the original gold standard of toxigenic culture for assessment of C. difficile detection methods. This month’s issue of On-Demand highlights the importance of using a proper reference point when evaluating new technologies. In the case of C.difficile, it is alcohol shock followed by broth enrichment and culture on pre-reduced media. In the case of MRSA detection in blood cultures, conventional susceptibility testing should be used.

Dealing with the Complexity of a Living Target

Friday, December 23, 2016 Published in On-Demand Fall 2010 Written by Ellen Jo Baron, Ph.D., D(ABMM), Prof. Emerita, Stanford University Director of Medical Affairs, Cepheid

CONCEPTS OF SENSITIVITY AND CONFIDENCE INTERVALS OF A NEW TEST RELATED TO COMPARATIVE (REFERENCE) ASSAYS

Example: Clostridium difficile tests

In their interpretation of laboratory test results, potentially risky practice patterns have been observed among some clinicians. If a laboratory test yields a positive result, clinicians tend to believe it and make treatment decisions based on that result. However, if the test result is negative but does not match their initial clinical impression, clinicians tend to discount the test result and continue their empiric therapy regimen or repeat the test to “prove” their initial diagnosis. Microbiologists often observe this phenomenon by examining physician ordering behavior with laboratory tests for Clostridium difficile.

The Cepheid HAI Consortium (A User-Based Resource)

Friday, December 23, 2016 Published in On-Demand Fall 2010 Written by Fred C. Tenover, Ph.D., D(ABMM), Senior Director for Scientific Affairs and Consortium Director

INTRODUCTION

The theme of the Cepheid Healthcare Associated Infection (HAI) Consortium is “Our Customers as Collaborators.” Our vision is to enlist our customers as partners to answer key questions about the changing epidemiology of healthcare-associated infections and resistance patterns of HAI-associated microorganisms. Consortium members provide Cepheid with organisms of interest during defined time periods. All isolates Cepheid receives have been de-identified and coded so that there is no link to patients’ protected health information. We have received and studied more than 500 isolates to date. The results of our studies are not only of scientific interest but they help Cepheid keep abreast of changing strain patterns that may influence our Xpert® assays. This has been particularly helpful in addressing the changing epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) isolates with the recognition of both “empty cassette” strains (where mecA is lost from the SCCmec cassette) and the emergence of SCCmec variants.