Prospective study of colonization and infection because of Pseudomonas aeruginosa in mechanically ventilated patients at a neonatal intensive care unit in China

Background: Ventilator-associated pneumonia (VAP) is an important nosocomial infection at neonatal intensive care units (NICU), frequently caused by Pseudomonas aeruginosa. A 6-month prospective study from January 2009 through June 2009 was performed to investigate the respective contribution of endogenous and exogenous transmission of P aeruginosa in the respiratory colonization or/and infection in the mechanically ventilated patients at a NICU to identify routes of lung infection with P aeruginosa and to assess risk factors for colonization or respiratory infection with P aeruginosa. Methods: Samples from oropharyngeal swab, tracheobronchial aspirates, gastric aspirate, and rectal swab were obtained in each patient after intubation and then twice a week. Surveillance cultures for the presence of P aeruginosa from environmental surfaces of the ICU were taken once every 5 days during the study period. Pulsed-field gel electrophoresis was used to characterize the clonal relatedness of the strains by SpeI-digested genomic DNA. Results: Eighteen patients (78.3%) had colonization of the upper respiratory tract. Sixteen (69.6%) patients with colonization of the respiratory tract were infected from other patients or environmental surfaces, which was considered exogenous, and, among strains causing pulmonary infection, there were 4 (50%) patients with exogenous infection. Eight of these developed VAP after a mean of 9 +/- 3.4 days. The incidence of P aeruginosa VAP on the unit was 6.2%. The respiratory tract was the earliest site of colonization in all patients of VAP. Low birth weight, duration of mechanical ventilation, previous ampicillin group use, and previous second-generation cephalosporins use were independently associated with patient-related acquisition of P aeruginosa. Conclusion: Our results confirm that the upper respiratory tract acts as an important reservoir of P aeruginosa colonization and infection in the mechanically ventilated patients and emphasize the importance of exogenous acquisition of P aeruginosa. A combination of early identification and eradication of airways colonization by P aeruginosa plus infection control measures may be the basis to prevent pulmonary infection.