Objective: To investigate the frequency and outcomes of ventilated patients with newly acquired large burdens of Pseudomonas aeruginosa and to test the hypothesis that large quantities of bacteria are associated with adverse patient outcomes.
Design: A prospective, single-center, observational, cohort study.
Setting: Medical-surgical intensive care units in a tertiary care university hospital.
Patients: All adult patients requiring ≥48 hrs of mechanical ventilation and identified as having newly acquired P. aeruginosa in their lower respiratory tracts between October 2002 and April 2006.
Measurements and Main Results: Daily surveillance cultures of endotracheal aspirates were performed on patients intubated ≥48 hrs; 69 patients with newly acquired P. aeruginosa were enrolled. Daily P. aeruginosa quantification of endotracheal aspirates was performed; clinical signs of infection were noted. Of 45 patients with high P. aeruginosa burdens (≥1,000,000 colony-forming units/mL in endotracheal aspirates; ≥10,000 colony-forming units/mL in bronchoalveolar-lavage), 17 (37.8%) patients did not meet clinical criteria for ventilator-associated pneumonia and had a statistically significant higher risk of death (adjusted hazard ratio, 37.53; 95% confidence interval, 3.79–371.96; p = 0.002) when compared with the patients who had P. aeruginosa ventilator-associated pneumonia. When excluding the ten patients who had ventilator-associated pneumonia attributed to bacteria other than P. aeruginosa or attributed to multiple bacteria including P. aeruginosa, the risk of death remained statistically significant (adjusted hazard ratio, 23.98; 95% confidence interval: 2.49–230.53; p = 0.006). Furthermore, more patients with high P. aeruginosa burdens secreted the type III secretion facilitator protein, PcrV (p = 0.01).
Conclusions: A group of patients with large burdens of P. aeruginosa who did not meet clinical criteria for ventilator-associated pneumonia had an increased risk of death when compared with patients who had high P. aeruginosa burdens and met ventilator-associated pneumonia criteria. Patients with high P. aeruginosa burden seemed to possess more virulent strains.