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Implications of C. difficile diagnostic testing. Not seeing the wood for the trees Warren Lowman Pathlink / Vermaak & Partners Pathologists Wits Donald Gordon Medical Centre Clinical Microbiology & Infectious Diseases, University of the Witwatersrand. Pubmed & C. difficile. 9298 hits - PowerPoint PPT Presentation
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Implications of C. difficile diagnostic testing
Not seeing the wood for the trees
Warren LowmanPathlink/ Vermaak & Partners Pathologists
Wits Donald Gordon Medical CentreClinical Microbiology & Infectious Diseases, University of the
Witwatersrand
ICU HC Surgical Medical Oncology0
20
40
60
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100
120
C. diff pos+C. diff requestsN
o.
Are we selecting accurately?
67.1 tests/ 10 000 pt bed days (range, 29 – 153)
C. difficile diagnostics…
1. We are floundering- survey of UK labs indicate >25 different algorithms
2. Multitude of different assays3. Impacts on our understanding of the
epidemiology of CDI.
Jan Feb Mar AprMay Jun Jul AugSeptOct Nov Dec0
2
4
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12
C. diff Rate/ 10 000 patient days
Rate (/10 000 pt days)2013 Cumulative rate
Salient points
1. Tested all faecal samples irrespective of request
2. Wide scope of practice3. Detection of 3 targets: bacterium; toxin; gene4. Predefined groups: diagnostic; severity5. Statistically very “sound”6. Diagnostic performance assessed in training
phase
Clinical relevance by assay
1. Data for 6522 inpatient episodes
Variable Grp1 vs Grp2 Grp1 vs Grp3
Mean WCC 0.0004 <0.0001
Died 0.022 <0.0001
Death rate 0.0195 0.0033
…clinical relevance by assay1. Same comparison using PCR as surrogate for
cytotoxigenic culture
Variable Grp1 vs Grp2 Grp1 vs Grp3
Mean WCC <0.0001 <0.0001
Died 0.004 <0.0001
Death rate 0.0317 0.0018
What’s best?
Performance GDH + EIA NAAT + EIA
Sensitivity 81.8% 82.9%
Specificity 99.5% 99.6%
PPV 91.6% 92.1%
NPV 98.9% 98.9%
C. difficile excretors…an issue?
Overtreatment…excessive antibiotic use!Cost…this all adds up
GDH EIA Toxin PCR
POSITIVE 14 7 14
NEGATIVE 11 18 11