What are the most common causes of cough?

Most Common Causes of Cough

Acute cough (lasting <3 weeks) is most commonly caused by viral upper respiratory tract infections, while chronic cough (lasting >8 weeks) is most frequently due to upper airway cough syndrome/postnasal drip (33.2%), asthma (15.8%), gastroesophageal reflux disease, or nonasthmatic eosinophilic bronchitis (5.4%). 1, 2, 3

Acute Cough (<3 weeks)

Viral upper respiratory tract infections are the predominant cause of acute cough, accounting for the vast majority of cases. 1, 3, 4

• Viral URTIs occur at rates of 2-5 episodes per adult per year and 7-10 episodes per year in school children, translating to approximately 120 million episodes annually in the UK. 1
• Cough is present in 40-50% of naturally acquired URTI cases. 1
• Common cold viruses cause self-limited illness that typically resolves within 2 weeks without requiring antimicrobial therapy. 5, 4
• Acute bronchitis (viral lower respiratory tract infection) is another common cause of acute cough. 4

Postinfectious cough is the most common etiology when acute cough persists beyond 3 weeks but less than 8 weeks (subacute cough). 2, 3

• Bordetella pertussis should be included in the differential diagnosis of subacute cough. 3

Chronic Cough (>8 weeks)

In nonsmokers not taking ACE inhibitors with normal chest radiographs, chronic cough has four primary causes, often occurring in combination: 3

Upper Airway Cough Syndrome/Postnasal Drip Syndrome

• Accounts for 33.2% of chronic cough cases. 2
• This is the single most common identifiable cause of chronic cough. 2

Asthma

• Responsible for 15.8% of chronic cough cases. 2
• May present as cough-variant asthma without typical wheezing. 3

Gastroesophageal Reflux Disease (GERD)

• A major contributor to chronic cough, often requiring intensive acid suppression with proton pump inhibitors for a minimum of 2 months. 1, 2

Nonasthmatic Eosinophilic Bronchitis

• Accounts for 5.4% of chronic cough cases. 2
• Characterized by eosinophilic airway inflammation without asthma physiology. 3

Drug-Induced Cough

ACE inhibitor-induced cough occurs in 5-50% of patients depending on ethnicity and should always be considered in patients taking these medications. 1, 2

• Other medications causing cough include beta-blockers, inhaled medications, chemotherapeutic agents, and aminoglycosides. 1, 2
• A therapeutic withdrawal trial of the suspected drug should be undertaken to determine if the cough resolves. 1, 2

Critical Diagnostic Pitfalls

Several life-threatening conditions can present with cough and must not be missed:

• Pulmonary embolism causes cough in nearly half of documented cases and can occasionally be the presenting complaint. 1, 2
• Pneumonia can present as acute cough and requires chest radiography for diagnosis. 3
• Congestive heart failure may present with cough as the sole manifestation. 1
• Mediastinal lesions can impinge on airways causing chronic cough. 1, 2

Algorithmic Approach to Evaluation

Duration-based classification guides the diagnostic approach:

1. For acute cough (<3 weeks): Assume viral URTI unless red flags present (hemoptysis, severe dyspnea, life-threatening symptoms). 1, 2

2. For subacute cough (3-8 weeks): Consider postinfectious etiology, including pertussis. 3

3. For chronic cough (>8 weeks): 1, 2

   • Verify patient is nonsmoker and not taking ACE inhibitors
   • Obtain mandatory chest radiography and spirometry 1
   • Systematically evaluate for upper airway cough syndrome, asthma, GERD, and eosinophilic bronchitis
   • Consider empiric treatment trials for common causes 2
   • If drug-induced cough suspected, perform therapeutic withdrawal trial 1, 2

The severity of cough should be quantified and treatment effects formally measured to guide management decisions. 1