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Identification of a Pseudo-Outbreak of Clostridium difficile Infection (CDI) and the Effect of Repeated Testing, Sensitivity, and Specificity on Perceived Prevalence of CDI

Published online by Cambridge University Press:  31 March 2016

Marina Litvin ,
Kimberly A. Reske ,
Jennie Mayfield ,
Kathleen M. McMullen ,
Peter Georgantopoulos ,
Susan Copper ,
Joan E. Hoppe-Bauer ,
Victoria J. Fraser ,
David K. Warren  and
Erik R. Dubberke
Marina Litvin
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
Kimberly A. Reske
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
Jennie Mayfield
Affiliation:
Departments of Infection Prevention and Control, Barnes-Jewish Hospital, St Louis, Missouri
Kathleen M. McMullen
Affiliation:
Departments of Infection Prevention and Control, Barnes-Jewish Hospital, St Louis, Missouri
Peter Georgantopoulos
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
Susan Copper
Affiliation:
Laboratories, Barnes-Jewish Hospital, St Louis, Missouri
Joan E. Hoppe-Bauer
Affiliation:
Laboratories, Barnes-Jewish Hospital, St Louis, Missouri
Victoria J. Fraser
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
David K. Warren
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
Erik R. Dubberke*
Affiliation:
Department of Medicine, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, Missouri
*
Division of Infectious Diseases, Washington University School of Medicine, 660 South Euclid Avenue, Box 8051, St Louis, MO 63110 (edubberk@im.wustl.edu)
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Abstract

Objective.

To describe a pseudo-outbreak of Clostridium difficile infection (CDI) caused by a faulty toxin assay lot and to determine the effect of sensitivity, specificity, and repeated testing for C. difficile on perceived CDI burden, positive predictive value, and false-positive results.

Design.

Outbreak investigation and criterion standard.

Patients.

Patients hospitalized at a tertiary care hospital who had at least 1 toxin assay for detection of C. difficile performed during the period from July 1, 2004, through June 30, 2006.

Methods.

The run control chart method and the x2 test were used to compare CDI rates and the proportion of positive test results before, during, and after the pseudo-outbreak. The effect of repeated testing was evaluated by using 3 hypothetical models with a sample of 10,000 patients and various assay sensitivity and specificity estimates.

Results.

In November of 2005, the CDI rate at the hospital increased from 1.5 to 2.6 cases per 1,000 patient-days (P< .01), and the proportion of positive test results increased from 13.6% to 22.1% (P< .01). An investigation revealed a pseudo-outbreak caused by a faulty toxin assay lot. A decrease of only 1.2% in the specificity of the toxin assay would result in a 32% increase in perceived incidence of CDI at this institution. When calculated by use of the manufacturer's stated specificity and sensitivity and this institution's testing practices, the positive predictive value of the test decreased from 80.6% to 4.1% for patients who received 3 tests.

Conclusion.

Specificity is as important as sensitivity when testing for CDI. False-positive CDI cases can drain hospital resources and adversely affect patients. Repeated testing for C. difficile should be performed with caution.

Type
Original Articles
Information
Infection Control & Hospital Epidemiology , Volume 30 , Issue 12 , December 2009 , pp. 1166 - 1171
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2009

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