Distinguishing Acute Bronchitis from Pneumonia
Acute bronchitis is diagnosed when a patient presents with acute cough (with or without sputum) lasting less than 3 weeks, but only after pneumonia has been excluded—the most critical diagnostic step since pneumonia requires specific antimicrobial therapy and carries significant morbidity and mortality if untreated. 1, 2
Clinical Algorithm for Differentiation
Step 1: Assess for Pneumonia Using Four Key Criteria
If ALL four of the following are absent, pneumonia is sufficiently unlikely that chest radiography can be omitted: 1, 2, 3
- Heart rate >100 beats/min
- Respiratory rate >24 breaths/min
- Oral temperature >38°C (100.4°F)
- Focal chest examination findings (consolidation, egophony, or fremitus)
If ANY of these four criteria are present, obtain a chest X-ray to rule out pneumonia. 1, 2
Step 2: Special Populations Requiring Lower Threshold
Even with fewer clinical findings present, obtain chest radiography in: 3
- Patients ≥65 years of age (elderly patients present with fewer symptoms but higher pneumonia risk) 1, 4
- Patients with COPD, diabetes, or heart failure 3
- Recent hospitalization, oral glucocorticoid use, or recent antibiotic use 3
Step 3: Additional Pneumonia Red Flags
The European Respiratory Society recommends suspecting pneumonia when acute cough is present PLUS any one of: 3
- New focal chest signs on examination
- Dyspnea or tachypnea
- Pulse rate >100 beats/min
- Fever lasting >4 days
- Temperature >38°C
Step 4: Consider CRP Testing When Available
CRP provides valuable diagnostic information: 3
- CRP <20 mg/L with symptoms >24 hours makes pneumonia highly unlikely
- CRP >100 mg/L makes pneumonia likely
Critical Diagnostic Pitfalls to Avoid
Do NOT assume purulent or green sputum indicates bacterial pneumonia requiring antibiotics. Sputum color reflects inflammatory cells from either viral or bacterial causes and does not reliably differentiate between bacterial and viral infections. 1, 2, 5
Do NOT routinely order viral cultures, sputum cultures, respiratory PCR, spirometry, or serum biomarkers (C-reactive protein, procalcitonin) in immunocompetent adults with suspected acute bronchitis. 2
Do NOT misdiagnose asthma as acute bronchitis. Approximately 40% of patients with acute bronchitis have transient bronchial hyperresponsiveness mimicking asthma, and in patients with recurrent "acute bronchitis" episodes (≥2 in past 5 years), 65% actually have mild asthma. 1, 3
Treatment Implications Based on Diagnosis
If Acute Bronchitis is Confirmed:
Antibiotics are NOT indicated for acute bronchitis in patients without chronic lung disease. Viruses cause >90% of acute bronchitis cases, and antibiotics provide only minimal benefit (reducing cough by approximately half a day) while causing adverse effects including allergic reactions, nausea, vomiting, and Clostridium difficile infection. 5, 6
The cough typically lasts 2-3 weeks, and patients should be counseled about this natural course. 5, 6
Antibiotics should only be considered if: 5
- Pertussis is suspected (to reduce transmission)
- Patient is at increased risk of developing pneumonia (age ≥65 years)
If Pneumonia is Confirmed:
Immediate empiric antimicrobial therapy is required based on local resistance patterns. Delayed appropriate antimicrobial therapy increases mortality. 4
For community-acquired pneumonia in adults appropriate for oral therapy, azithromycin (500 mg once daily for 3 days) is effective against Chlamydophila pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, and Streptococcus pneumoniae. 7
Azithromycin should NOT be used in patients with pneumonia who have: 7
- Moderate to severe illness
- Cystic fibrosis
- Nosocomial infections
- Known or suspected bacteremia
- Requirement for hospitalization
- Elderly or debilitated status
- Significant underlying health problems (immunodeficiency, functional asplenia)
High-Risk Populations: Special Considerations
Elderly Patients (≥65 years)
Maintain high suspicion for pneumonia in elderly patients, as this population presents with fewer respiratory and non-respiratory symptoms, making clinical diagnosis more challenging. 1, 4
Lower threshold for chest radiography even without all four pneumonia criteria present. 3
Young Children
For pediatric acute otitis media and community-acquired pneumonia, azithromycin (12 mg/kg once daily for 5 days) is effective when oral therapy is appropriate. 7
Patients with Chronic Respiratory Disease
For acute exacerbations of chronic bronchitis (AECB), bacterial pathogens (H. influenzae, M. catarrhalis, S. pneumoniae) are more common. 8
Azithromycin (500 mg once daily for 3 days) demonstrated 85% clinical cure rate for AECB, comparable to 10 days of clarithromycin. 7
Fluoroquinolones should be first-line for AECB in patients with: 8
- Complicated chronic bronchitis with co-morbid illness
- Severe obstruction (FEV₁ <50%)
- Age >65 years
- Recurrent exacerbations