The role of anaerobes in patients with ventilator-associated pneumonia and aspiration pneumonia: a prospective study

Chest. 1999 Jan;115(1):178-83. doi: 10.1378/chest.115.1.178.


Context: Aspiration of oropharyngeal material, with its high concentration of anaerobic bacteria, has been implicated in the pathogenesis of both ventilator-associated pneumonia (VAP) and aspiration pneumonitis (AP). Consequently, patients with these disorders are usually treated with antimicrobial agents with anaerobic activity.

Objective: To determine the incidence of anaerobic bacteria in patients with VAP and AP.

Design: Prospective, nonrandomized, interventional study.

Setting: University-affiliated community teaching hospital.

Patients and interventions: We performed sequential blind protected specimen brush (PSB) sampling and mini-BAL in 143 patients with 185 episodes of suspected VAP and 25 patients with AP who required mechanical ventilation. Quantitative aerobic and anaerobic cultures were performed on all specimens. Pneumonia was considered to be present when either > 500 cfu/mL cultured from blind PSB sampling or > 5,000 cfu/mL cultured from mini-BAL were present.

Results: Using the predefined criteria, bacterial pneumonia was diagnosed in 63 of 185 suspected VAP episodes (34%) and 12 of 25 patients with AP (48%). At least one dose of an antibiotic was given in the 24 h prior to bacteriologic sampling in 106 suspected VAP episodes (57%) and in 12 patients with AP (48%). More than one pathogen was isolated from 11 VAP and four AP patients. Pseudomonas aeruginosa, Staphylococcus aureus, and enteric Gram-negative organisms were isolated most frequently from patients with VAP. In the patients with AP, enteric Gram-negative organisms were isolated in patients with GI disorders and Streptococcus pneumoniae and Haemophilus influenzae predominated in patients with "community-acquired" aspiration. Only one anaerobic organism was isolated from the entire group of patients; Veillonella paravula was isolated from a blind PSB specimen in a patient with suspected aspiration pneumonia.

Conclusion: Despite painstaking effort, we were able to isolate only one anaerobic organism (nonpathogenic) from this group of patients. The spectrum of aerobes in patients with VAP was similar to that reported in the literature. The organisms found in patients with AP was a reflection of the organisms likely to colonize the oropharynx. The use of antibiotics with anaerobic coverage may not be necessary in patients with suspected VAP and AP. Furthermore, penicillin G and clindamycin may not be the antibiotics of choice in patients with AP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Antibiotic Prophylaxis
  • Bacteria, Anaerobic / drug effects
  • Bacteria, Anaerobic / isolation & purification*
  • Bacteriological Techniques
  • Cross Infection / diagnosis*
  • Cross Infection / drug therapy
  • Cross Infection / microbiology
  • Female
  • Hospitals, Community
  • Hospitals, Teaching
  • Humans
  • Intensive Care Units
  • Male
  • Microbial Sensitivity Tests
  • Middle Aged
  • Oropharynx / microbiology
  • Pneumonia, Aspiration / diagnosis*
  • Pneumonia, Aspiration / drug therapy
  • Pneumonia, Aspiration / microbiology
  • Pneumonia, Bacterial / diagnosis*
  • Pneumonia, Bacterial / drug therapy
  • Pneumonia, Bacterial / microbiology
  • Prospective Studies
  • Ventilators, Mechanical*