Usefulness of quantitative cultures of BAL fluid for diagnosing nosocomial pneumonia in ventilated patients

Study objective: To evaluate the role of quantitative cultures of BAL for diagnosing nosocomial pneumonia in mechanically ventilated patients. Design: Cohort study. Setting: Medical ICU, Hopital Bichat, Paris, France, an academic tertiary care center. Patients: A total of 141 episodes of suspected lung infection in 84 consecutive patients mechanically ventilated for 48 h or more. Measurements and results: Microbiologic findings obtained using BAL were compared with those obtained with protected specimen brush (PSB) samples and their operating characteristics were determined, The level of qualitative agreement between BAL and PSB specimen cultures was high, with 83% of the organisms isolated in PSB specimens being recovered simultaneously from BAL fluid. In addition, the results of quantitative BAL and PSB cultures were significantly correlated (rho=0.46, p <0.0001). Fifty-seven cases of pneumonia were diagnosed based on the following criteria: PSB sample yielding greater than or equal to 10(3) cfu/ml of at least one microorganism and/or greater than or equal to 5% of cells containing intracellular bacteria on direct examination of BAL. The operating characteristics of BAL fluid cultures were determined using different ways to report the results and over a range of values, The discriminative value of 10(4) cfu/ml was found to be an optimal threshold, with a sensitivity of 82% (95% confidence interval [CI], 76 to 88) and a specificity of 84.5% (95% CI, 79 to 90). Conclusions: These results indicate that BAL fluid cultures can offer a sensitive and specific means to diagnose pneumonia in ventilated patients and may provide relevant information about the causative pathogens.