What causes a chronic cough after a viral infection?

Causes of Chronic Cough After Viral Infection

The primary causes of chronic cough after viral infection include persistent airway inflammation, transient bronchial hyperresponsiveness, and excessive mucus hypersecretion resulting from extensive disruption of epithelial integrity in the respiratory tract. 1

Pathophysiology of Post-Infectious Cough

Post-infectious cough occurs when a viral respiratory infection leads to:

• Extensive disruption of respiratory epithelial integrity
• Widespread airway inflammation (upper and/or lower airways)
• Excessive mucus hypersecretion
• Transient airway and cough receptor hyperresponsiveness
• Impaired mucociliary clearance

Bronchoscopy findings in patients with post-viral cough (e.g., after influenza A) show desquamation of epithelial cells down to the basement membrane, with high percentages of lymphocytes and neutrophils in BAL fluid 1.

Common Secondary Mechanisms

Several secondary mechanisms can develop and perpetuate chronic cough after the initial viral infection:

1. Upper Airway Cough Syndrome (UACS) - Persistent inflammation of the nose and paranasal sinuses (previously called postnasal drip syndrome) 1

2. Transient Bronchial Hyperresponsiveness - Can mimic asthma symptoms temporarily 1

3. Gastroesophageal Reflux Disease (GERD) - May develop as a complication of vigorous coughing 1

4. Non-asthmatic Eosinophilic Bronchitis (NAEB) - Characterized by eosinophilic infiltration of the bronchial tree without asthma symptoms 1, 2

Special Consideration: Bordetella pertussis

One particularly virulent form of post-infectious cough is caused by Bordetella pertussis infection, characterized by:

• Paroxysms of coughing
• Post-tussive vomiting
• Inspiratory whooping sound

This infection is highly contagious and requires specific antibiotic treatment with macrolides when identified early 1.

Diagnostic Timeline

The American College of Chest Physicians defines post-infectious cough as:

• Subacute cough: Lasting 3-8 weeks following viral infection 1
• If cough persists beyond 8 weeks, other diagnoses should be considered 1, 2

Diagnostic Approach

When evaluating chronic cough after viral infection:

1. Rule out other common causes if cough persists beyond 8 weeks:

   • Upper airway cough syndrome
   • Asthma or cough variant asthma
   • GERD
   • Non-asthmatic eosinophilic bronchitis 1, 2

2. Consider specialized testing if standard treatments fail:

   • Induced sputum analysis for eosinophils (to identify NAEB)
   • Evaluation for sensory neuropathy of the laryngeal nerve 3

Treatment Algorithm

1. First-line treatment: Inhaled ipratropium bromide (36 mcg, 2 puffs four times daily) 2

2. Second-line treatment: Add inhaled corticosteroids if no improvement with ipratropium 2

3. Third-line treatment: Consider dextromethorphan (15-30 mg three times daily) if cough persists and affects quality of life 2

4. For refractory cases: Consider neuromodulators (gabapentin or pregabalin), particularly if sensory neuropathy is suspected 2, 3

Important Clinical Pearls

• Antibiotics have no role in post-infectious cough unless there is evidence of bacterial superinfection (e.g., bacterial sinusitis or early B. pertussis infection) 1, 2

• Patient education is crucial - explain that post-viral cough is expected to resolve but may take several weeks 2

• Avoid respiratory irritants such as tobacco smoke and air pollution 2

• Warning signs requiring immediate medical attention include:

  • Hemoptysis
  • Breathlessness
  • Prolonged fever
  • Underlying medical conditions 2

• Cough hypersensitivity syndrome may explain why some patients develop chronic cough after viral infections while most recover completely 4

Differences Between Adults and Children

In children, chronic cough patterns differ from adults:

• Rarely due to GERD, postnasal drip, or asthma
• More commonly due to specific identifiable causes
• Symptomatic treatment is rarely needed or effective 5