A 62-year-old man with COPD presents with acute onset fever (39.2°C), productive cough with purulent sputum, and dyspnea for 3 days. Chest X-ray shows patchy infiltrates in the right lower and middle lobes with a bronchial distribution. Which investigation is most appropriate to confirm the diagnosis and guide antimicrobial therapy?

## Investigation of Choice in Bronchopneumonia **Key Point:** Sputum culture and Gram stain is the gold standard for microbiological diagnosis and antibiotic susceptibility testing in bronchopneumonia. ### Why Sputum Culture is Correct Bronchopneumonia presents with: - Patchy, multifocal infiltrates (often bilateral, lower lobes) - Bronchial distribution pattern - Rapid progression in patients with underlying lung disease (COPD) Sputum examination provides: 1. **Direct identification** of causative organism (Gram stain morphology) 2. **Culture** for definitive organism isolation 3. **Antimicrobial susceptibility** for targeted therapy 4. **Non-invasive** collection method ### Diagnostic Approach in Pneumonia | Investigation | Indication | Yield | Invasiveness | |---|---|---|---| | Sputum culture & Gram stain | Outpatient/ward bronchopneumonia | High (>80%) | Non-invasive | | Blood culture | Sepsis, bacteremia risk | Moderate (10–20%) | Minimally invasive | | HRCT chest | Atypical presentation, complications | High (anatomical detail) | Non-invasive, imaging | | BAL (bronchoscopy) | Immunocompromised, no sputum | High | Invasive | | Serum procalcitonin | Prognostication, severity | Moderate | Non-invasive | **Clinical Pearl:** In community-acquired bronchopneumonia with productive cough, a good-quality sputum sample (>25 WBCs, <10 epithelial cells per low-power field) is diagnostic and cost-effective. **High-Yield:** Bronchopneumonia in COPD patients is commonly caused by *Streptococcus pneumoniae*, *Haemophilus influenzae*, and *Moraxella catarrhalis* — organisms that grow readily on routine culture media. ### Why Other Investigations Are Secondary - **HRCT:** Provides anatomical detail but does NOT identify organism; reserved for complications or atypical cases - **BAL:** Invasive; reserved for immunocompromised patients or when sputum cannot be obtained - **Procalcitonin:** Prognostic marker, not diagnostic; does not guide organism-specific therapy