title: The appropriate diagnostic threshold for ventilator-associated pneumonia using quantitative cultures.
abstract: BACKGROUND
  The use of quantitative cultures of the bronchoalveolar lavage (BAL) effluent to distinguish between posttraumatic inflammatory response and ventilator-associated pneumonia (VAP) is becoming more common. However, the diagnostic threshold of either 10 or 10 colonies/mL remains debatable. Because mortality from VAP is related to treatment delay, some have chosen a lower diagnostic threshold (>10 colonies/mL). This may result in unnecessary antibiotic use with its sequelae: increased resistant organisms, antibiotic-related complications, and increased costs. The purpose of this study is to determine the optimal diagnostic threshold for VAP diagnosis using quantitative cultures of the BAL effluent.
  
  
  METHODS
  Data on patients with fiberoptic bronchoscopy with BAL are maintained in a prospectively collected database at our Level I trauma center. This database was reviewed for timing and frequency of BAL and the colony counts of each organism identified. Indication for bronchoscopy was clinical evidence of VAP. VAP was defined as >10 colonies/mL in the BAL effluent. A false-negative BAL was defined as any patient who had <10 colonies/mL and developed VAP with the same organism up to 7 days after the previous culture.
  
  
  RESULTS
  Over a 46-month period, 526 patients underwent 1,372 fiberoptic bronchoscopy procedures with BAL. Of these, 72% were male patients, 91% followed blunt injury, and mean age and Injury Severity Score were 43 years and 30, respectively. Overall mortality was 14%. There were 1,898 organisms identified (42% were gram-positive and 58% were gram-negative). VAP was diagnosed in 38% of BAL. Overall, there were 43 episodes in 38 patients defined as false-negative (3%). The false-negative rate was 9% in patients with 10 organisms. The most common false-negative organisms were Pseudomonas and Acinetobacter species.
  
  
  CONCLUSIONS
  The VAP diagnostic threshold for quantitative BAL in trauma patients should be >10 colonies/mL. One may consider a threshold of >10 colonies/mL in severely injured patients with Pseudomonas or Acinetobacter species.
authors.affiliation: Department of Surgery, University of Tennessee Health Science Center, Memphis, Tennessee, USA. mcroce@utmem.edu
authors.forename: Martin A
authors.initials: MA
authors.lastname: Croce
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Fabian
authors.forename: Eric W
authors.initials: EW
authors.lastname: Mueller
authors.forename: George O
authors.initials: GO
authors.lastname: Maish
authors.forename: Jordy C
authors.initials: JC
authors.lastname: Cox
authors.forename: Tiffany K
authors.initials: TK
authors.lastname: Bee
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Boucher
authors.forename: G Christopher
authors.initials: GC
authors.lastname: Wood
mesh_terms: D000328:Adult; D017677:Age Distribution; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology*; D015169:Colony Count, Microbial; D003428:Cross Infection / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology*; D003937:Diagnosis, Differential; D004351:Drug Resistance; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005334:Fever / Q000382:microbiology; D017052:Hospital Mortality; D006801:Humans; D015601:Injury Severity Score; D007964:Leukocytosis / Q000382:microbiology; D007970:Leukopenia / Q000382:microbiology; D008297:Male; D008826:Microbial Sensitivity Tests; D018410:Pneumonia, Bacterial / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology*; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D013714:Tennessee / Q000453:epidemiology; D013997:Time Factors; D014193:Trauma Centers; D012122:Ventilators, Mechanical / Q000009:adverse effects*