Bacterial colonization patterns in mechanically ventilated patients with traumatic and medical head injury - Incidence, risk factors, and associationwith ventilator-associated pneumonia

We prospectively evaluated the relation of upper airway, lower airway, and gastric colonization patterns with the development of pneumonia and its eti ology in 48 patients with surgical (n = 25) and medical (n = 23) head injur y. Initial colonization was assessed by cultures of nasal and pharyngeal sw abs, tracheobronchial aspirates, gastric juice, and bronchoscopically retri eved protected specimen brush. Follow-up colonization was determined until the end points extubation, suspected ventilator-associated pneumonia (VAP), or death. The initial colonization rate at any site at ICU admission was 3 9/47 (83%). It mainly accounted for Group I pathogens (Streptococcus pneumo niae, Staphylococcus aureus, Hemophilus influenzae) of the upper and lower airways. At follow-up, colonization rates with Group II pathogens (Gram-neg ative enteric baciili and Pseudomonas spp.) increased significantly. The hi gh initial bacterial toad with Group I pathogens of the upper airways and t rachea decreased during Days 2 to 4, whereas that of Group II pathogens inc reased. Upper airway colonization was an independent predictor of follow-up tracheobronchial colonization (odds ratio [OR], 9.9; 95% confidence interv al [CI], 1.8 to 56.3 for initial colonization with Group I pathogens; OR, 2 3.9; 95% CI, 3.8 to 153.3 for follow-up colonization with Group II pathogen s). Previous (short-term) antibiotics had a protective effect against colon ization with Group I pathogens of the lower respiratory tract (OR, 0.2; 95% CT, 0.05 to 0.86), but they were a risk factor for colonization with Group Il pathogens (OR, 6.1; 95% CI, 1.3 to 29). Initial tracheobronchial coloni zation with Group I pathogens was associated with a higher probability of e arly onset pneumonia (OR, 4.1; 95% CI, 0.7 to 23.3), whereas prolonged anti biotic treatment (> 24 h) independently predicted late-onset pneumonia (OR, 9.2; 95% CI, 1.7 to 51.3). We conclude that patients with head injury are colonized in the airways mainly by Group I pathogens early in the evolution of illness. The upper airways represent the main reservoir for subsequent lower airway colonization with Group I pathogens. Previous (short-term) ant ibiotic treatment is protective against initial tracheobronchial colonizati on with Group I pathogens, but it represents a risk factor for subsequent l ower airway colonization by Group II pathogens.