How to diagnose acute bronchitis?

Diagnosing Acute Bronchitis

Acute bronchitis is a clinical diagnosis made in patients presenting with sudden onset of cough (with or without sputum) lasting less than 3 weeks, after excluding pneumonia, asthma exacerbation, chronic bronchitis exacerbation, and other serious conditions. 1

Primary Diagnostic Criteria

The diagnosis requires:

• Acute cough as the predominant symptom, with or without sputum production 1
• Duration less than 3 weeks (distinguishes from chronic cough) 1
• Absence of pneumonia and other serious respiratory conditions 1

Key Clinical Features

• Cough may be productive or nonproductive 1, 2
• Purulent (yellow or green) sputum does NOT indicate bacterial infection and should not influence diagnosis or antibiotic decisions 1, 3
• May have accompanying upper respiratory symptoms (sore throat, rhinorrhea) 1
• Transient bronchial hyperresponsiveness occurs in approximately 40% of cases 1

Critical Step: Ruling Out Pneumonia

The most important diagnostic task is excluding pneumonia, which requires different management and carries significant morbidity and mortality if untreated. 1

When Chest X-ray is NOT Needed

If ALL four of the following are absent, pneumonia is sufficiently unlikely that chest radiography can be omitted: 1

1. Heart rate > 100 beats/min
2. Respiratory rate > 24 breaths/min
3. Oral temperature > 38°C (100.4°F)
4. Focal chest examination findings (consolidation, egophony, or fremitus)

When Chest X-ray IS Indicated

Obtain chest radiography if ANY of the following are present: 4

• Any of the four vital sign/examination abnormalities listed above 1, 4
• Age ≥ 60 years (elderly patients have atypical presentations with lower prevalence of typical symptoms) 1, 4
• Hemoptysis 4
• Cough persisting > 3 weeks 1, 4
• C-reactive protein > 100 mg/L (if obtained) 4

Important caveat: In elderly patients, maintain a high index of suspicion for pneumonia even with fewer symptoms, as this population presents atypically. 1, 5

Routine Testing is NOT Recommended

For immunocompetent adults with suspected acute bronchitis, do NOT routinely order: 1

• Viral cultures or serologic assays 1
• Sputum cultures or analyses 1
• Respiratory tract samples for viral PCR 1
• Spirometry or peak flow measurement 1
• Serum C-reactive protein or procalcitonin 1

Rationale: The responsible organism is rarely identified in clinical practice, and testing does not change management in uncomplicated cases. 1

Special Epidemiologic Considerations

Consider specific pathogens based on exposure history: 1

• Pertussis: Contact with confirmed case, severe paroxysmal cough, whooping sound, or post-tussive vomiting 1
• Mycoplasma or Chlamydia pneumoniae: Outbreaks in military personnel or college students 1

Differential Diagnosis to Exclude

Before confirming acute bronchitis, rule out: 1, 2

Asthma or Cough-Variant Asthma

• Consider if: Recurrent episodes of "bronchitis," cough worsening at night or with cold/exercise exposure, or cough persisting > 3 weeks 1, 3
• Transient bronchial hyperresponsiveness in acute bronchitis typically resolves within 6 weeks 1

Acute Exacerbation of Chronic Bronchitis

• Different disease entity requiring different management 1
• Occurs in patients with known chronic bronchitis/COPD 2

Common Cold

• Predominantly upper respiratory symptoms with less prominent cough 1

Heart Failure Exacerbation

• Particularly important in elderly patients with cardiac history 2

Common Diagnostic Pitfalls

Avoid these errors: 1, 3

• Do NOT assume purulent sputum indicates bacterial infection - sputum color reflects inflammatory cells from either viral or bacterial causes and should not guide antibiotic decisions 1, 3
• Do NOT order chest X-rays in healthy, non-elderly adults with normal vital signs and normal lung examination - pneumonia is uncommon (only 4%) in this population 4
• Do NOT misdiagnose recurrent acute bronchitis - consider underlying asthma instead 1, 3

Diagnostic Algorithm Summary

1. Patient presents with acute cough (< 3 weeks duration) 1
2. Check vital signs and perform chest examination 1
3. If ALL four pneumonia criteria absent AND patient < 60 years: Diagnose acute bronchitis clinically, no chest X-ray needed 1, 4
4. If ANY pneumonia criteria present OR age ≥ 60 years: Obtain chest X-ray to rule out pneumonia 1, 4
5. If cough persists > 3 weeks: Reconsider diagnosis and evaluate for asthma, upper airway cough syndrome, GERD, or other chronic conditions 3, 4