1315. Effect of Nucleic Acid Amplification Testing on Population-based Incident Rates of Clostridium difficile Infection (CDI)
Session: Oral Abstract Session: Challenges in C. difficile Infection Surveillance
Saturday, October 20, 2012: 11:15 AM
Room: SDCC 29 ABCD

Nucleic acid amplification tests (NAATs) targeting toxin genes of C. difficile have higher sensitivity than enzyme immunoassays (EIA) and are being adopted by clinical laboratories.  The use of NAAT is likely to increase detection of CDI, but the magnitude of the increases on incidence rates is unknown.


CDI case counts (case defined as a positive C. difficile stool specimen by toxin or molecular assay from a resident of the surveillance catchment area without a prior positive assay in the past 8 weeks) and laboratory testing methods from population-based surveillance operating across 35 counties in 10 U.S. states during 2009-2011 were evaluated.  Labs that changed from EIA to NAAT as first line testing (“switch labs”) were compared to labs that only used EIA during the evaluation period (“non-switch labs”) which served as controls. The median ratio of CDI case counts for switch labs during equivalent bimonthly time intervals post- and pre- switch, to control for seasonal variation, was compared to the median ratio for non-switch labs (same catchment area, same time).  A one-sided non-parametric median test was used for comparison.  The change in CDI incidence in each catchment area attributable to NAAT was calculated as the ratio of the switch lab median ratio over the non-switch lab median ratio, by EIP site.  The proportions of stools tested that were C. difficile positive in the 3 months pre- and post- NAAT in switch labs were compared using a Mid-P exact test.


Five switch labs from 3 states (CA, GA, CO) were compared to a total of 43 non-switch labs. The number of months evaluated ranged from 14 to 24. The post/pre median ratios of case counts for switch labs were greater than the median ratios for non-switch labs in all states:  CA: 1.78 vs. 1.0 (P=0.008); GA: 1.59 vs. 1.0 (P=0.01); CO: 1.87 vs. 0.99 (P=0.006), respectively.  The relative percent increases in CDI incidence attributed to NAAT were 78% in CA, 59% in GA and 89% in CO.  Percent of specimens testing positive increased from 8% to 19% (P<0.0001) in the 3 months after implementation of NAAT.


We expect that labs switching to NAAT will increase population-based incidence of CDI by 59%-89%.  Analysis and interpretation of CDI rates require adjustment for more sensitive testing methods. 

Carolyn Gould, MD1, Jonathan Edwards, MStat1, Jessica Cohen, MPH1,2, L. Clifford Mcdonald, MD1, Monica M. Farley, MD3, Helen Johnston, MPH4, Lucy Wilson, MD5, Samir Hanna, MD6, Lisa Winston, MD7, Stacy Holzbauer, DVM8, Carol Lyons, MPH9, Erin Phipps, DVM10,11, Gary Hollick, PhD12, Zintars G. Beldavs, MS13, Dale Gerding, MD, FIDSA14, Fernanda Lessa, MD1 and CDC's Clostridium difficile Infection Surveillance Investigators, (1)Centers for Disease Control and Prevention, Atlanta, GA, (2)Atlanta Research and Education Foundation, Atlanta, GA, (3)Atlanta Veterans Medical Center, Atlanta, GA, (4)Colorado Department of Public Health and Environment, Denver, CO, (5)Maryland Department of Health and Mental Hygiene, Baltimore, MD, (6)Tennessee Department of Health, Nashville, TN, (7)University of California, San Francisco/San Francisco General Hospital, San Francisco, CA, (8)CDC CEFO assigned to the Minnesota Department of Health, St. Paul, MN, (9)Connecticut Emerging Infections Program, New Haven, CT, (10)New Mexico Emerging Infections Program, Albuquerque, NM, (11)University of New Mexico, Albuquerque, NM, (12)Emerging Infections Program, University of Rochester Medical Center, Rochester, NY, (13)Oregon Health Authority, Portland, OR, (14)Edward Hines, Jr. Veterans Affairs Hospital, Hines, IL


C. Gould, None

J. Edwards, None

J. Cohen, None

L. C. Mcdonald, None

M. M. Farley, None

H. Johnston, None

L. Wilson, None

S. Hanna, None

L. Winston, None

S. Holzbauer, None

C. Lyons, None

E. Phipps, None

G. Hollick, None

Z. G. Beldavs, None

D. Gerding, ViroPharma: Consultant and Patents licensed to ViroPharma, Consulting fee and Licensing agreement or royalty
Merck: Scientific Advisor, Consulting fee and Research grant
Optimer: Scientific Advisor, Consulting fee and Grant recipient
Cubist: Scientific Advisor, Consulting fee
Pfizer: Consultant, Consulting fee
GlaxoSmithKline: Scientific Advisor, Consulting fee
BioRelix: Scientific Advisor, Consulting fee
Novartis: Scientific Advisor, Consulting fee
Cangene: Consultant, Consulting fee
Actelion: Scientific Advisor, Consulting fee and Research grant
Eurofins Medinet: Research Contractor, Research grant
GOJO: Research Contractor, Research grant
Sanofi Pasteur: Research Contractor, Research grant

F. Lessa, None

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