Detection of Nosocomial Lung Infection in Ventilated Patients: Use of a Protected Specimen Brush and Quantitative Culture Techniques in 147 Patients

Abstract

To determine the usefulness of samples obtained by bronchoscopy using a protected specimen brush and evaluated by quantitative culture techniques in establishing the diagnosis of nosocomial pneumonia in patients requiring mechanical ventilation, we prospectively studied 147 ventilated patients suspected of having nosocomial pneumonia because of the presence of a new pulmonary infiltrate and purulent tracheal secretions. Positive cultures of protected brush specimens (>103 cfu/ml) were found in only 45 patients (31%). Subsequent follow-up confirmed the diagnosis of pneumonia in 34 of 45 patients, and in only 4 of 45 patients was a positive culture firmly established to be a false positive result. No patient with <103 cfu/ml was subsequently shown to have had pneumonia, and the diagnosis was definitely excluded in 72 to 102 patients by the absence of pneumonia at autopsy or recovery without antibiotic therapy. In contrast, when 16 clinical variables were evaluated by stepwise logistic regression analysis, no combination could be identified that was useful in distinguishing patients with bacterial pneumonia. Furthermore, when the actual costs of evaluation and therapy of our patients were compared with the projected costs entailed in treating all patients suspected of having pneumonia with antibiotics, evaluation using the protected specimen brush and quantitative cultures was less expensive after only 6 days of treatment. These results suggest that the appearance of pulmonary infiltrates and purulent tracheal secretions does not result from bacterial pneumonia in a majority of patients. Patients requiring antimicrobial therapy can be accurately identified using samples obtained with a protected specimen brush and evaluated with quantitative culture techniques, but cannot be distinguished on clinical grounds alone. Evaluation of patients suspected of having nosocomial pneumonia by this procedure avoids the unnecessary use of antibiotics in such patients, thereby reducing toxicity associated with antibiotic use and the overall cost of patient management.