A 62-year-old man with a 40 pack-year smoking history presents with progressive dyspnea and chronic productive cough. Spirometry confirms COPD (FEV₁ 35% predicted). He is started on inhaled therapy. Which is the most common cause of acute exacerbation in COPD patients?

Explanation

## Most Common Cause of COPD Exacerbation **Key Point:** Respiratory tract infection (RTI) accounts for approximately 50–70% of acute exacerbations of COPD, making it the single most frequent trigger in clinical practice. ### Pathophysiology of RTI-Triggered Exacerbation 1. Viral or bacterial infection of the lower respiratory tract 2. Increased airway inflammation and mucus production 3. Bronchial hyperresponsiveness and airflow obstruction worsens 4. Impaired mucociliary clearance in COPD patients ### Common Causative Organisms | Organism Type | Examples | Frequency | |---|---|---| | Viral | Rhinovirus, influenza, parainfluenza, RSV | ~30% of exacerbations | | Bacterial | *Haemophilus influenzae*, *Streptococcus pneumoniae*, *Moraxella catarrhalis* | ~50% of exacerbations | | Atypical | *Chlamydia pneumoniae*, *Mycoplasma pneumoniae* | ~10% of exacerbations | **High-Yield:** The classic triad of COPD exacerbation is increased dyspnea, increased sputum volume, and increased sputum purulence — all consistent with infection. ### Why RTI Is Most Common - COPD patients have impaired immune responses and abnormal airway flora - Colonization with pathogenic bacteria is common in moderate-to-severe COPD - Seasonal variation (winter peaks) correlates with viral respiratory season - Vaccination (influenza, pneumococcal) reduces exacerbation frequency, confirming infection's role **Clinical Pearl:** A patient with COPD presenting with acute dyspnea, increased sputum purulence, and fever should be treated empirically for bacterial respiratory infection pending culture results. [cite:Harrison 21e Ch 297]