title: Impact of the type of diagnostic assay on Clostridium difficile infection and complication rates in a mandatory reporting program.
abstract: BACKGROUND
  Most Clostridium difficile infection (CDI) surveillance programs neither specify the diagnostic method to be used nor stratify rates accordingly. We assessed the difference in healthcare-associated CDI (HA-CDI) incidence and complication rates obtained by 2 validated diagnostic methods.
  
  
  METHODS
  This was a prospective cohort study of patients for whom a C. difficile test was ordered between 1 August 2010 and 31 July 2011. All specimens were tested in parallel by a commercial polymerase chain reaction (PCR) assay targeting toxin B gene tcdB, and a 3-step algorithm detecting glutamate dehydrogenase and toxins A and B by enzyme immunoassay and cell culture cytotoxicity assay (EIA/CCA). CDI incidence rate ratios were calculated using univariate Poisson regression.
  
  
  RESULTS
  A total of 1321 stool samples were tested during a period totaling 95 750 patient-days. Eighty-five HA-CDI cases were detected by PCR and 56 cases by EIA/CCA (P = .01). The overall incidence rate was 8.9 per 10 000 patient-days (95% confidence interval [CI], 7.1-10.9) by PCR and 5.8 per 10 000 patient-days (95% CI, 4.4-7.4) by EIA/CCA (P = .01). The incidence rate ratio comparing PCR and EIA/CCA was 1.52 (95% CI, 1.08-2.13; P = .015). Overall complication rate was 27% (23/85) when CDI was diagnosed by PCR and 39% (22/56) by EIA/CCA (P = .16). Cases detected by PCR only were less likely to develop a complication of CDI compared with cases detected by both PCR and EIA/CCA (3% vs 39%, respectively; P < .001).
  
  
  CONCLUSIONS
  Performing PCR instead of EIA/CCA is associated with a >50% increase in the CDI incidence rate. Standardization of diagnostic methods may be indicated to improve interhospital comparison.
authors.affiliation: Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, Canada. yves.longtin@crchuq.ulaval.ca
authors.forename: Yves
authors.initials: Y
authors.lastname: Longtin
authors.forename: Sylvie
authors.initials: S
authors.lastname: Trottier
authors.forename: Gilles
authors.initials: G
authors.lastname: Brochu
authors.forename: Bianka
authors.initials: B
authors.lastname: Paquet-Bolduc
authors.forename: Christophe
authors.initials: C
authors.lastname: Garenc
authors.forename: Vilayvong
authors.initials: V
authors.lastname: Loungnarath
authors.forename: Catherine
authors.initials: C
authors.lastname: Beaulieu
authors.forename: Danielle
authors.initials: D
authors.lastname: Goulet
authors.forename: Jean
authors.initials: J
authors.lastname: Longtin
mesh_terms: D000465:Algorithms; D001431:Bacteriological Techniques / Q000379:methods* / Q000706:statistics & numerical data; D002170:Canada / Q000453:epidemiology; D016009:Chi-Square Distribution; D016360:Clostridioides difficile / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D003015:Clostridium Infections / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology; D003428:Cross Infection / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology; D005243:Feces / Q000382:microbiology; D006801:Humans; D007124:Immunoenzyme Techniques; D015994:Incidence; D019221:Mandatory Reporting; D016133:Polymerase Chain Reaction; D011446:Prospective Studies