Clinical significance of borderline quantitative protected brush specimen culture results

In patients with clinical suspicion of pneumonia, quantitative cultures of protected brushing specimens (PBS) yielding > or = 10(3) CFU/ml of at least one microorganism have been found useful for differentiating airway colonization and lung infection, especially in mechanically ventilated patients. The amount of secretions collected by protected catheter brushing is small and difficult to determine accurately. Thus, the clinical significance of PBS cultures yielding organisms in concentrations > or = 10(2) but < 10(3) CFU/ml, in the absence of active antimicrobial treatment, is unknown. The 34 consecutive results of PBS cultures yielding organisms in concentrations > or = 10(2) but < 10(3) CFU/ml in 30 patients under mechanical ventilation or weaned for < or = 4 days were prospectively studied. No patients were receiving agents active on the organism recovered. In 5 cases, the diagnosis of pneumonia was ruled out by recovery without treatment (n = 4) or negative postmortem lung cultures (n = 1). A second PBS was cultured in 29 episodes (2.7 +/- 1.8 days after the first PBS). In 12 instances (Group 1), cultures of the second PBS yielded > or = 10(3) CFU/ml of the same organism as that found in the first PBS (S. pneumoniae, 1; S. aureus, 1; H. influenzae, 1; E. coli, 1; P. aeruginosa, 4; and A. baumannii, 4), and these patients were therefore treated with appropriate antibiotics. A total of 17 patients had a negative repeat PBS culture (no growth or trivial concentrations) and were considered free of pneumonia and given no antibiotic treatment for this episode.(ABSTRACT TRUNCATED AT 250 WORDS)