bronchitis

Acute bronchitis is most commonly caused by viral infections (e.g., rhinovirus, influenza, RSV, adenovirus) and typically follows an upper respiratory tract infection. It presents with cough (with or without sputum), which can persist for 1-3 weeks even after other symptoms resolve, low-grade fever, and chest discomfort. Treatment is supportive (antitussives, NSAIDs, hydration); antibiotics are generally not indicated unless bacterial superinfection or pertussis is suspected. Chronic bronchitis is a clinical diagnosis defined by productive cough for at least 3 months in 2 consecutive years, resulting from chronic irritant exposure (most commonly cigarette smoke) causing hypertrophy and hyperplasia of mucus-secreting bronchial glands (increased Reid index >50%), goblet cell hyperplasia, and chronic inflammation with mucus hypersecretion. It is one of the two classic phenotypes of COPD (along with emphysema) and is sometimes called the "blue bloater" phenotype due to cyanosis from hypoxemia/hypercapnia and peripheral edema from cor pulmonale, though there is significant overlap with emphysema in real patients. Pathophysiology involves airway obstruction from mucus plugging and bronchial wall thickening, leading to V/Q mismatch, hypoxemia, and secondary polycythemia. Patients are at increased risk for recurrent pulmonary infections, cor pulmonale, and respiratory failure. Spirometry shows an obstructive pattern (decreased FEV1/FVC ratio). Management includes smoking cessation (most important intervention), bronchodilators (beta-agonists, anticholinergics), inhaled corticosteroids for frequent exacerbations, pulmonary rehabilitation, and long-term oxygen therapy if hypoxemic. Acute exacerbations of chronic bronchitis are often triggered by infections (H. influenzae, S. pneumoniae, M. catarrhalis, or viruses) and treated with bronchodilators, corticosteroids, and antibiotics if criteria met (increased sputum purulence, volume, or dyspnea).