Microbiological testing and outcome of patients with severe community-acquired pneumonia

Study objectives: The study documents the impact of microbiological investigations on therapeutic decisions and outcome in patients with severe community-acquired pneumonia (SCAP). Design: Retrospective analysis of prospectively collected data. Setting: ICUs in two teaching Spanish hospitals. Patients: Two hundred four consecutive patients admitted to intensive care with SCAP. Interventions: None. Measurements and results: One hundred six patients required intubation, while 98 other patients did not (81 of these patients were managed with noninvasive mechanical ventilation). The microbiologic diagnosis was established in 57.3% of patients. The most common pathogens were Streptococcus pneumoniae, Legionella pneumophila, and Haemophilus influenzae. Pseudomonas (6.6.% vs 1.0%, p < 0.05) and Legionella (15.1% vs 7.1%, p < 0.05) were more frequently documented in intubated patients. Overall mortality was 23.5% (44.3% in intubated patients), with S pneumoniae (n = 7), Pseudomonas aeruginosa (n = 7), and L pneumophila (n = 5) being the most common lethal pathogens. Bacteriological investigation led to changes in antibiotic prescription in 41.6% of patients, including 11 patients (5%) in whom initial treatment was ineffective against the microbial isolates. The most frequent reason for changes was simplification of therapy in 65 episodes (31.8%). Conclusions: We conclude that microbiological testing is fully justified in patients with SCAP, because identifying the causative agent and adjusting treatment both impact on patient outcome. Our findings suggest that intubated patients should be empirically treated for Pseudomonas and Legionella while awaiting bacteriology results.