Endotracheal Bacteriology and Ventilator Associated Pneumonia Risks

Data published in BMC Infectious Diseases showed that heavy tracheal colonization aided the identification of patients at higher risk of developing a corresponding Staphylococcus aureus or Gram-negative ventilator-associated pneumonia (VAP). Detection of bacterial endotracheal aspirate positivity tended to precede VAP.

This prospective observational study was performed at 3 intensive care units (ICUs) at the Lahey Hospital and Medical Center (Burlington, Massachusetts) between June 2014 and June 2015. The study aims were to determine whether the detection and quantification, by means of endotracheal aspirate, of bacterial airway colonization is useful in identifying mechanically ventilated patients who are at risk of developing VAP.

A total of 240 patients from the ICUs who were mechanically ventilated for >2 days were enrolled, and clinical data and endotracheal aspirate samples were collected.

Pathogenic bacteria were isolated from 125 patients, with the most common being S aureus at 56.8%, followed by Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli at 35.2% combined. Results also showed that VAP was diagnosed in 85 patients: 44 of whom had a bacterial pathogen, 18 in whom it was associated with S aureus, 18 who had Gram-negative only bacteria, and 5 in whom it was associated with other Gram-positive or mixed species. There was a higher percentage of patients heavy colonization with S aureus (32.4%) who developed VAP, compared with those who were less significantly colonized (17.6%).

A similar pattern was seen among patients with heavy or light colonization with Gram-negative pathogens, 30.0% and 0.0%, respectively. Endotracheal aspirate detection of S aureus proceeded S aureus VAP by approximately 4 days, and the first detection of Gram-negative organisms occurred 2.5 days before Gram-negative VAP. A patient’s likelihood of acquiring VAP was also associated with significantly longer duration of mechanical ventilation and hospitalization, regardless of the microbiologic cause.

One limitation of this study was the use of solely endotracheal aspirate samples to assign a bacterial pathogen to a VAP episode. Deep respiratory sample microbiology such as bronchoalveolar lavage or a protected specimen brush was not included. In addition, whereas data were collected prospectively, VAP diagnoses were assigned retrospectively, and the diagnosis was not made by the treating physician but instead was determined by the sponsor based on generally accepted criteria. The data are also limited in their generalizability because of the small sample size that was drawn from a single center. Also, an analysis of the contribution of each bacterial species other than S aureus to VAP was limited because of the low case numbers.

Investigators concluded that, “continuous [semi-quantative analysis of endotracheal aspirate] surveillance cultures from the start of mechanical ventilation for those patients expected to be ventilated for more than 2 days to identify bacterial pathogens may be useful to identify patients at high risk for bacterial VAP infection.” Further, that tracheal colonization proceeds the clinical signs and symptoms of VAP means there is a window of opportunity for VAP prevention. The investigators also concluded that the data support ongoing efforts to identify high-risk populations with bacterial colonization for targeted preventive measures.

Reference

Kabak E, Hudcova J, Magyarics Z, et al. The utility of endotracheal aspirate bacteriology in identifying mechanically ventilated patients at risk for ventilator associated pneumonia: a single-center prospective observational study. BMC Infect Dis. 2019;19:756.