Acute Bronchitis: Definition, Diagnosis, Etiology, and Management

Definition

• Acute bronchitis is defined as an acute lower‑respiratory‑tract infection presenting with cough (with or without sputum) that lasts no longer than three weeks and occurs without clinical or radiographic evidence of pneumonia. 1

Essential Diagnostic Criteria (clinical exclusion)

• In otherwise healthy individuals, the diagnosis requires all of the following: sudden‑onset cough, symptom duration ≤ 3 weeks, absence of pneumonia on exam and imaging, and exclusion of other causes such as the common cold, acute asthma, or COPD exacerbation. 1

Etiology

• Viral origin in > 90 % of cases – most commonly influenza A/B, parainfluenza, respiratory syncytial virus, coronavirus, rhinovirus, and adenovirus. 2
• Bacterial infection is rare (< 10 %), limited mainly to Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis, and Bordetella parapertussis. 2
• Transient bronchial hyper‑reactivity occurs in approximately 40 % of previously healthy patients during the acute episode. 3

Clinical Differentiation from Other Conditions

Pneumonia Exclusion (healthy adults < 70 y)

• Pneumonia is considered highly unlikely when all of the following are absent: heart rate < 100 bpm, respiratory rate < 24 breaths/min, oral temperature < 38 °C, and normal chest examination (no focal consolidation, crackles, egophony, or tactile fremitus). 1

Common Cold vs. Acute Bronchitis

• The common cold is dominated by upper‑airway symptoms (nasal congestion, rhinorrhea, sneezing, sore throat), whereas acute bronchitis is characterized principally by cough. 4

Underlying Asthma

• About one‑third of patients presenting with acute cough have previously undiagnosed asthma that is often misattributed to acute bronchitis. 4
• Patients reporting ≥ 2 similar “bronchitis” episodes in the past 5 years have a 65 % likelihood of underlying mild asthma. 4

Common Misconceptions

Purulent Sputum

• A purulent or yellow‑green sputum color reflects inflammatory cells and desquamated epithelium, not the presence of bacterial infection, and therefore should not automatically trigger antibiotic therapy. 5

Expected Clinical Course

• The cough of acute bronchitis typically persists for 2–3 weeks; persistence beyond 3 weeks warrants evaluation for alternative diagnoses such as post‑infectious cough, upper‑airway cough syndrome, asthma, or gastro‑esophageal reflux disease. 1

Populations Excluded from the “Uncomplicated” Definition

• Individuals with underlying chronic lung disease (e.g., COPD, bronchiectasis), congestive heart failure, or immunocompromise (e.g., AIDS, chemotherapy) are not classified as having uncomplicated acute bronchitis. 1

Recommended (and Non‑Recommended) Investigations

• Routine testing is not indicated in immunocompetent patients with suspected acute bronchitis, unless abnormal vital signs or physical findings are present. Specifically, the following are not recommended routinely:
  
  • Chest radiography (except when clinical signs suggest pneumonia)
  • Spirometry or peak expiratory flow measurement
  • Sputum culture
  • Viral PCR panels
  • Serum C‑reactive protein or procalcitonin levels
  • [All above] – supported by Chest guideline statements. 6

Acute Bronchitis: Evidence‑Based Management

Diagnostic Considerations

• In otherwise healthy adults (≤70 years) presenting with a short‑duration cough, normal vital signs, and no focal chest findings, acute bronchitis is the most likely diagnosis and further testing (e.g., chest radiography, sputum culture) is unnecessary. 7
• When a patient has throat discomfort without painful swallowing, the symptom is typically a manifestation of the concurrent viral upper‑respiratory infection rather than a separate bacterial pharyngitis. 7
• Applying the modified Centor criteria—absence of fever, tonsillar exudates, and tender cervical adenopathy, with the presence of cough—yields fewer than three positive criteria, indicating that rapid streptococcal testing is not required. 7

Antibiotic Stewardship

• Antibiotics should not be prescribed for acute bronchitis unless there is clinical suspicion of pneumonia; the condition is overwhelmingly viral in origin. 7
• Macrolide antibiotics used for acute bronchitis are associated with a significantly higher rate of adverse events compared with placebo, providing no clinical benefit. 7

Symptomatic Treatment Options

• Cough suppressants (e.g., dextromethorphan or codeine) may be offered for comfort. 7
• Expectorants such as guaifenesin can be used to aid mucus clearance. 7
• First‑generation antihistamines (e.g., diphenhydramine) are appropriate for symptomatic relief. 7
• Oral decongestants (e.g., phenylephrine) may be employed to reduce nasal congestion. 7
• Warm fluids are recommended to soothe the throat and improve comfort. 7
• Short‑acting β‑agonists (e.g., albuterol) have no demonstrated benefit in patients without underlying asthma or chronic obstructive pulmonary disease. 7

Expected Clinical Course & Patient Education

• Symptomatic therapy does not shorten the duration of acute bronchitis; the cough usually persists for 2–3 weeks, after which it resolves spontaneously. 7
• Over‑the‑counter medications used for symptom control have a low incidence of minor adverse effects (e.g., nausea, headache, drowsiness). 7

Work‑Related Guidance

• Provide a brief work‑exemption note (typically 1–2 days) to accommodate the self‑limited viral illness, emphasizing that no additional medical testing or antibiotics are required. 7