What are the criteria to diagnose acute bronchitis?

Diagnostic Criteria for Acute Bronchitis

Acute bronchitis is diagnosed clinically in patients presenting with acute cough (with or without sputum) lasting less than 3 weeks, after excluding pneumonia, asthma exacerbation, COPD exacerbation, and other serious respiratory conditions. 1

Core Diagnostic Criteria

The diagnosis requires three essential elements:

• Acute cough as the predominant symptom (with or without sputum production) 1
• Duration less than 3 weeks, which distinguishes it from chronic cough 1
• Absence of pneumonia and other serious respiratory conditions after appropriate clinical evaluation 2, 1

The American College of Chest Physicians emphasizes that acute bronchitis should only be diagnosed when there is no evidence of pneumonia, common cold, acute asthma, or COPD exacerbation 2

Critical Step: Excluding Pneumonia

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

Clinical Decision Rule for Chest X-ray

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

• Heart rate > 100 beats/min
• Respiratory rate > 24 breaths/min
• Oral temperature > 38°C (100.4°F)
• Focal chest examination findings (consolidation, egophony, fremitus)

However, obtain a chest X-ray if any of these criteria are present OR if the patient is ≥60 years old, regardless of vital signs. 1, 3 Elderly patients have higher pneumonia incidence, increased mortality risk, and atypical presentations 3

Routine Testing is NOT Recommended

For immunocompetent adult outpatients with suspected acute bronchitis, do NOT routinely order: 2, 1

• Chest X-ray (unless pneumonia criteria met)
• Spirometry or peak flow measurement
• Sputum for microbial culture
• Respiratory tract samples for viral PCR
• Serum C-reactive protein (CRP)
• Procalcitonin

These investigations add no diagnostic value over clinical assessment alone in straightforward cases 2

When to Consider Targeted Investigation

If acute bronchitis persists or worsens, advise the patient to seek reassessment and consider targeted investigations: 2

• Chest X-ray to exclude delayed pneumonia
• Sputum culture if bacterial superinfection suspected
• Peak expiratory flow rate recordings if asthma suspected
• Complete blood count and inflammatory markers (CRP)

Critical Differential Diagnoses to Exclude

Before confirming acute bronchitis, systematically rule out: 2, 1

• Pneumonia (most critical—use vital signs and chest exam)
• Asthma or cough-variant asthma (consider if wheezing present or recurrent episodes—65% of patients with recurrent "bronchitis" actually have mild asthma) 2
• COPD exacerbation (in smokers or those with known COPD)
• Acute exacerbation of chronic bronchitis (in patients with chronic productive cough)
• Bronchiectasis exacerbation (if history of recurrent infections)
• Common cold/acute rhinosinusitis (predominantly upper respiratory symptoms)
• Heart failure exacerbation (if cardiac history, orthopnea, edema)
• Pertussis (if prolonged paroxysmal cough or known exposure)

Common Diagnostic Pitfalls to Avoid

Do NOT assume purulent (green/yellow) sputum indicates bacterial infection requiring antibiotics. 1 Sputum color reflects inflammatory cells from either viral or bacterial causes and should not guide antibiotic decisions 1

Do NOT order chest X-rays in healthy, non-elderly adults (<60 years) with normal vital signs and normal lung examination, as pneumonia is uncommon (only 4%) in this population 3

Recognize that recurrent episodes of "acute bronchitis" may actually represent undiagnosed asthma. 2 In retrospective studies, 65% of patients with recurrent physician-diagnosed acute bronchitis episodes were found to have mild asthma 2

Typical Clinical Presentation

While not required for diagnosis, patients commonly present with: 4, 5

• Cough (92% of cases)
• Phlegm production (63%)
• Runny nose (50%)
• Throat pain (50%)
• Pharyngeal erythema on exam (45%)
• Wheezes or rhonchi (18-17%)

Symptoms typically last approximately 2-3 weeks, which is important for patient counseling 4