Impact of Changes in Clostridium difficile Testing Practices on Stool Rejection Policies and C. difficile Positivity Rates across Multiple Laboratories in the United States

Abstract

We describe the adoption of nucleic acid amplification tests (NAAT) for Clostridium difficile diagnosis and their impact on stool rejection policies and C. difficile positivity rates. Of the laboratories with complete surveys, 51 (43%) reported using NAAT in 2011. Laboratories using NAAT had stricter rejection policies and increased positivity rates. Clostridium difficile infection (CDI) continues to be an important public health problem due to its high incidence, morbidity, and medical care costs (1, 2). Rapid and reliable C. difficile diagnosis is an important component in preventing transmission of C. difficile (2-4). The traditional toxin enzyme immunoassays (EIA) used by many clinical laboratories are known to have a low sensitivity; however, they have been widely adopted due to their simplicity, their low cost, their rapid turnaround time, and, until recently, lack of a better alternative (4, 5). Since 2008, the U.S. Food and Drug Administration has approved eight nucleic acid amplification tests (NAAT) for C. difficile testing (6). These NAAT have sensitivities ranging from 84% to 94% and short turnaround times compared with toxigenic stool culture, making them attractive to clinical laboratories (7,8). Although laboratory practice guidelines discourage repeat C. difficile testing and testing of formed stools regardless of the assay type (9-12), it is unclear how well these guidelines have been adopted by U.S. clinical laboratories and if the introduction of NAAT has resulted in changes to stool rejection policies.(This study was presented in part at the 2012 IDWeek Meeting, San Diego, CA, 17 to 21 October 2012.)From 1 November 2011 to 31 January 2012, we surveyed 121 laboratories serving 11.2 million people in 10 U.S. states participating in the CDC's Emerging Infections Program populationbased CDI surveillance (13). We compared stool rejection policies of laboratories using NAAT to those of laboratories that do not, assessed changes in stool rejection policies after NAAT implementation, and evaluated the impact of NAAT adoption on C. difficile positivity rates. A NAAT laboratory was defined as a laboratory using NAAT as a first-or second-line test. A non-NAAT laboratory was defined as a laboratory using assays other than NAAT, such as toxin EIA, glutamate dehydrogenase (GDH), cell cytotoxicity neutralization assays, or toxigenic culture. Data collection included current testing practices, changes to testing algorithms and stool rejection policies in the past year, and the number of stool specimens tested and the number of stools positive for C. difficile in the 3 months before and after NAAT implementation.The chi-square test and the Wilcoxon signed-rank test were used to evaluate differences.Surveys were completed by 120 (99%) of the 121 laboratories surveyed, representing 88 inpatient and 32 outpatient laboratories. Fifty-one (43%) laboratories reported using NAAT; of these, 27 (53%) switched to NAAT as either a first-line (n ϭ 20) or second-line (n ϭ 7) test in 2011. Prior to the switch, 24 (89%) lab...

Clostridium difficile PCR Cycle Threshold Predicts Free Toxin

“…Compared to current practices at our institution and other U.S. hospitals where nearly all patients with positive C. difficile PCR results are treated for CDI (16,17), reporting C T toxin result in addition to PCR result has the potential to reduce anti-C. difficile therapy by 45.8% based on results of this study (143 of 312 PCR-positive samples were C T toxin negative), if only toxin-positive patients are treated. This approach has the potential to have far-reaching impact as stand-alone C. difficile NAAT has been widely adopted for CDI diagnosis in the United States (18). Further studies are needed to implement C T toxin reporting under routine clinical practice and measure its impact on provider behavior, patient outcomes, and antibiotic stewardship.…”

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