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Implications of C. difficile Diagnostic Testing: Addressing Pre-test Probability and Assay Variability

This publication explores the challenges of C. difficile diagnostic testing, emphasizing the often-overlooked importance of pre-test probability and positive predictive value (PPV). With a significant variation in testing algorithms across UK laboratories and various assay types available, it affects our understanding of the epidemiology of Clostridium difficile infection (CDI). We will discuss the clinical relevance of different diagnostic performance measures and the consequences of overtreatment and excessive antibiotic usage stemming from testing inaccuracies.

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Implications of C. difficile Diagnostic Testing: Addressing Pre-test Probability and Assay Variability

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  1. 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

  2. Pubmed & C. difficile • 9298 hits • + Clinical trials = 330 • + Diagnosis = 169 • + Testing = 20

  3. Clinical relevance… 2 key issues that are largely ignored: • Pre-test probability • PPV

  4. Are we selecting accurately? 67.1 tests/ 10 000 pt bed days (range, 29 – 153)

  5. C. difficile diagnostics… • We are floundering- survey of UK labs indicate >25 different algorithms • Multitude of different assays • Impacts on our understanding of the epidemiology of CDI.

  6. The “best” study Lancet Infect Dis 2013 Diagnostic assays Study design Clinical data

  7. Salient points • Tested all faecal samples irrespective of request • Wide scope of practice • Detection of 3 targets: bacterium; toxin; gene • Predefined groups: diagnostic; severity • Statistically very “sound” • Diagnostic performance assessed in training phase

  8. Clinical relevance by assay • Data for 6522 inpatient episodes

  9. …clinical relevance by assay • Same comparison using PCR as surrogate for cytotoxigenic culture

  10. The point…clinically

  11. So what do we do about diagnosis?

  12. What’s best?

  13. The implications CLINICAL OUTCOME MANAGEMENT TOXIN POSITIVITY DIAGNOSTIC ASSAY

  14. C. difficile excretors…an issue? Overtreatment…excessive antibiotic use! Cost…this all adds up

  15. 3-stage algorithm Not CDAD GDH CDAD EIA Toxin 8% NAAT Not CDAD C. difficile excretor

  16. Thank you!

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