Comparison of semi-quantitative endotracheal aspirates to quantitative non-bronchoscopic bronchoalveolar lavage in diagnosing ventilator-associated pneumonia

Respir Care. 2009 Nov;54(11):1453-61.


Background: Current strategies for diagnosing ventilator-associated pneumonia (VAP) favor the use of quantitative methods; however, semi-quantitative cultures of endotracheal aspirates are still commonly used.

Methods: The microbiological results of patients with suspected VAP who had both quantitative cultures with non-bronchoscopic bronchoalveolar lavage (BAL) and semi-quantitative cultures of endotracheal aspirate obtained within 24 hours of each other were retrospectively reviewed and compared, using a quantitative threshold of >or=10(4) colony-forming units/mL as a reference standard.

Results: 256 patients with paired cultures were identified. Concordance between endotracheal aspirate (any growth of pathogens) and non-bronchoscopic BAL was complete in 58.2% and completely discordant in 23.8%. The sensitivity and specificity of endotracheal aspirate were 65.4% and 56.1%, which improved to 81.2% and 61.9% when antibiotic management decisions were considered in the analysis. Twenty-six patients had endotracheal aspirate cultures that were falsely negative for pathogens, with 61.5% of these patients demonstrating growth of non-fermenting Gram-negative rods or methicillin-resistant Staphylococcus aureus (MRSA) on non-bronchoscopic BAL. Overall, 45 patients (17.5%) among the entire cohort had false positive endotracheal aspirate cultures, with 19 of these patients (42.2%) demonstrating growth of non-fermenting Gram-negative rods or MRSA.

Conclusions: Semi-quantitative cultures of endotracheal aspirate are poorly concordant with quantitative cultures obtained via non-bronchoscopic BAL. Although the performance of endotracheal aspirate improves when antibiotic treatment is considered, guiding therapy on the basis of semi-quantitative cultures may still result in failure to identify potentially multiple-drug-resistant pathogens, and would also tend to promote excessive antibiotic usage. Our data support the use of quantitative cultures in diagnosing VAP.

Publication types

  • Comparative Study

MeSH terms

  • Aged
  • Bronchoalveolar Lavage Fluid / microbiology
  • Bronchoalveolar Lavage*
  • False Negative Reactions
  • False Positive Reactions
  • Female
  • Gram-Negative Bacteria / isolation & purification
  • Gram-Positive Bacteria / isolation & purification
  • Humans
  • Male
  • Middle Aged
  • Pneumonia, Ventilator-Associated / diagnosis*
  • Pneumonia, Ventilator-Associated / microbiology
  • Predictive Value of Tests
  • Retrospective Studies
  • Sensitivity and Specificity
  • Suction
  • Trachea / microbiology*