What is the difference between acute bronchitis and pneumonia in terms of diagnosis and treatment?

Distinguishing Acute Bronchitis from Pneumonia

The key distinction is that pneumonia requires the presence of infiltrates on chest radiograph, while acute bronchitis is diagnosed when chest radiograph is normal despite cough and respiratory symptoms. 1

Clinical Criteria to Rule Out Pneumonia

For healthy immunocompetent adults younger than 70 years, pneumonia is unlikely when ALL of the following are absent: 1

• Tachycardia (heart rate >100 beats/min)
• Tachypnea (respiratory rate >24 breaths/min)
• Fever (oral temperature >38°C)
• Abnormal chest examination findings (rales, egophony, or tactile fremitus)

When all four vital sign and examination criteria are normal, the likelihood of pneumonia is sufficiently reduced that chest radiography is usually not necessary. 1 However, this clinical decision rule has a specificity of approximately 67% and sensitivity of 75%, which exceeds physician judgment alone (specificity 58%). 1

Diagnostic Approach

When to Obtain Chest Radiography

Chest radiograph is essential when: 2

• Any of the four clinical criteria above are present (tachycardia, tachypnea, fever, or abnormal lung examination)
• Fever is present with productive cough and systemic symptoms 2
• The patient has risk factors for complications (age >75 years, cardiac failure, insulin-dependent diabetes, serious neurological disorder) 1

Common Diagnostic Pitfall

Purulent or colored (green/yellow) sputum does NOT indicate bacterial pneumonia or the need for antibiotics. 1 Sputum purulence results from inflammatory cells or sloughed mucosal epithelial cells and occurs with both viral and bacterial infections. 1 The presence or absence of purulent sputum does not reliably differentiate between bacterial and viral infections. 3

Key Diagnostic Features

Acute Bronchitis Characteristics

• Cough (with or without sputum) lasting up to 3 weeks 1
• Normal chest radiograph (by definition) 1
• Predominantly viral etiology (>90% of cases) 1, 4
• May have mild constitutional symptoms 1
• Self-limited course 1

Pneumonia Characteristics

• Infiltrates on chest radiograph (required for diagnosis) 1
• More likely with abnormal vital signs and focal consolidation findings 1
• Requires antibiotic treatment due to bacterial etiology and 10-20% risk of complicated disease course 1

Treatment Implications

Acute Bronchitis Management

Antibiotics are NOT indicated for uncomplicated acute bronchitis. 1 Systematic reviews show antibiotics provide minimal benefit (reducing cough duration by only 0.5 days) while exposing patients to adverse effects including allergic reactions, nausea, vomiting, and Clostridium difficile infection. 5, 6

Symptomatic treatment options include: 1

• Cough suppressants (dextromethorphan or codeine) for dry, bothersome cough
• Patient education that cough typically lasts 2-3 weeks 5, 3, 6

Do NOT prescribe: 1

• Expectorants, mucolytics, or antihistamines (no consistent evidence of benefit)
• Inhaled bronchodilators (no benefit without underlying asthma or COPD) 1

Pneumonia Management

Antibiotics ARE indicated for suspected or confirmed pneumonia due to bacterial etiology and significant complication risk. 1

Critical Clinical Caveat

If cough persists beyond 3 weeks, acute bronchitis is no longer the diagnosis and other conditions must be considered, including asthma, pertussis, or other chronic causes. 1, 7