Superinfections in Pseudomonas aeruginosa ventilator-associated pneumonia.

Background: Data on superinfections in patients with ventilator-associated pneumonia vary, but different pathogens are typically studied as a single category. We studied the incidence of superinfections and the outcomes of patients with superinfections in Pseudomonas aeruginosa ventilator-associated pneumonia.

Methods: Sixty patients with Pseudomonas aeruginosa ventilator-associated pneumonia were initially treated appropriately. On day three of follow-up, bronchoalveolar lavage was collected. For Pseudomonas aeruginosa species that reached >104 colony forming units/ml upon follow-up, bronchoalveolar lavage pulsed gel field electrophoresis was applied. Accordingly, Pseudomonas aeruginosa was identified as a superinfection when isolates were genetically unrelated to those isolated at study entry or as a persistence of infection when isolates were closely related.

Results: Upon follow-up, 15 (25%) patients displayed superinfections with Pseudomonas aeruginosa that was resistant to the initial antibiotic regimen. Forty-five (75%) patients did not have a superinfection upon follow-up. Among these patients, 18 (30%) had a persistent infection , as determined by the significant counts of initial Pseudomonas aeruginosa isolates that had developed resistance, and 27 (45%) had persistence in which insignificant counts of initial Pseudomonas aeruginosa isolates remained sensitive to the initial antibiotics. Antibiotic treatment was adjusted for patients with superinfections and persistence with the development of resistance. The Simplified Acute Physiology Score (45.1±4.9 versus 43±4.9, P=0.38), the Sequential Organ Failure Assessment (4.13±2.5 versus 4.7±2.7, P=0.53) and mortality (20% versus 17.7%, P~1.00) were comparable on day-14 for patients with and without a superinfection.

Conclusion: For Pseudomonas aeruginosa ventilator-associated pneumonia, superinfections are not uncommon as early as day three, but they do not increase mortality.