Can Bronchitis Be Bacterial?
Yes, bronchitis can be bacterial, but the answer depends critically on whether you're dealing with acute or chronic bronchitis—these are fundamentally different diseases with different microbiology.
Acute Bronchitis: Rarely Bacterial
In acute uncomplicated bronchitis, bacterial causes are rare, accounting for less than 10% of cases, and routine antibiotic treatment is not recommended. 1
Established Bacterial Causes
The only bacteria definitively linked to acute bronchitis in otherwise healthy individuals are: 1
- Mycoplasma pneumoniae (< 1% in routine cases)
- Chlamydophila pneumoniae (< 1% in routine cases)
- Bordetella pertussis
- Bordetella parapertussis
What About Common Respiratory Bacteria?
There is no evidence that Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis cause acute bronchitis in healthy adults without underlying lung disease. 1 These organisms may colonize the upper airways, and their presence in sputum likely represents colonization rather than acute infection. 1
Viral Predominance
More than 90% of acute bronchitis cases are caused by viruses, including influenza A and B, parainfluenza, respiratory syncytial virus, coronavirus, adenovirus, and rhinovirus. 1, 2
Clinical Pitfall: Purulent Sputum
Purulent sputum does NOT indicate bacterial infection. 1 Purulence occurs when inflammatory cells or sloughed epithelial cells are present and can result from either viral or bacterial infection. This is a common misconception that leads to inappropriate antibiotic prescribing.
Chronic Bronchitis: Bacterial Role in Exacerbations
In patients with chronic bronchitis, bacteria play a significant role during acute exacerbations, though the baseline disease involves chronic colonization. 1
Bacterial Colonization vs. Infection
During stable periods, many patients with chronic bronchitis (especially current smokers) are colonized with: 1
- Streptococcus pneumoniae
- Moraxella catarrhalis
- Haemophilus influenzae
Acute Exacerbations
It is estimated that 50-70% of acute exacerbations of chronic bronchitis are caused by bacterial infections. 3 Molecular typing studies show that acute exacerbations are frequently associated with acquisition of a new strain of a previously colonizing organism, supporting a causative bacterial role. 1
Viral infections account for approximately one-third of exacerbations and predispose to bacterial superinfection by impairing mucociliary clearance and bacterial killing by macrophages. 1
Key Distinction
Acute exacerbation of chronic bronchitis is a different disease than acute bronchitis. 1 The bacterial pathogens and treatment approach differ fundamentally between these conditions.
Diagnostic Approach
For Acute Bronchitis
Viral cultures, serologic assays, and sputum analyses should not be routinely performed because the responsible organism is rarely identified in clinical practice. 1 Gram stain and culture of sputum do not reliably detect M. pneumoniae, C. pneumoniae, or B. pertussis. 1
For Chronic Bronchitis Exacerbations
Diagnosis is clinical, based on sudden deterioration with increased cough, sputum production, sputum purulence, and/or worsening dyspnea, often preceded by upper respiratory symptoms. 1 Other conditions (pneumonia, pulmonary embolism, heart failure) must be excluded. 1
Treatment Implications
Acute Bronchitis
Routine antibiotic treatment of uncomplicated acute bronchitis is not recommended, regardless of duration of cough. 1 Antibiotics do not consistently impact duration or severity of illness. 1
Chronic Bronchitis Exacerbations
Antibiotics are appropriate for acute exacerbations, particularly in patients with comorbidities, severe obstruction (FEV1 < 50%), age > 65 years, or recurrent exacerbations. 4, 3 Fluoroquinolones, cephalosporins, or beta-lactam/beta-lactamase inhibitor combinations are reasonable choices. 5, 4, 3