Diagnosing Acute Bronchitis
Acute bronchitis is a clinical diagnosis made in patients presenting with acute cough (with or without sputum) lasting 1-3 weeks, after ruling out pneumonia, common cold, acute asthma, and COPD exacerbation through history and physical examination alone—no routine testing is needed. 1, 2
Essential Diagnostic Criteria
To diagnose acute bronchitis, the patient must have:
- Sudden onset of cough with or without sputum production lasting no more than 3 weeks 1
- No clinical or radiographic evidence of pneumonia 1
- Common cold, acute asthma, and COPD exacerbation have been ruled out 1
- Often preceded by viral upper respiratory symptoms (rhinorrhea, sore throat) 2
Critical Step: Ruling Out Pneumonia
The most important diagnostic task is distinguishing bronchitis from pneumonia, which has significant morbidity and mortality if untreated. 1
A chest radiograph can be safely avoided if ALL four of the following are absent: 1, 2, 3
- Heart rate >100 beats/min
- Respiratory rate >24 breaths/min
- Oral temperature >38°C
- Chest examination findings of focal consolidation, egophony, or fremitus
If any of these findings are present, obtain a chest radiograph to evaluate for pneumonia, particularly in elderly patients who may have fewer symptoms despite having pneumonia. 3
Physical Examination Findings
On examination, patients with acute bronchitis may have:
- Wheezing or crackles on auscultation 2
- Normal vital signs (absence of high fever, tachycardia, tachypnea) 2
- Productive cough with purulent sputum (though this does NOT distinguish bronchitis from pneumonia) 1, 3
What NOT to Do
Do not routinely perform: 1, 2, 3
- Viral cultures or serologic assays (the responsible organism is rarely identified in clinical practice)
- Sputum analyses
- Chest radiographs (if pneumonia criteria above are absent)
- Laboratory tests or serum markers
Common Diagnostic Pitfalls
Beware of misdiagnosing asthma as acute bronchitis:
- Approximately one-third of patients presenting with acute cough labeled as "acute bronchitis" actually have acute asthma 1
- If a patient has had at least two similar episodes of "acute bronchitis" in the past 5 years, 65% can be identified as having mild asthma 1, 2
- Consider asthma if there are recurrent episodes, and perform pulmonary function testing 2
The clinical distinction between acute bronchitis and the common cold is often difficult or impossible to make, as they share many symptoms. 1
Special Epidemiologic Clues
Consider specific pathogens based on epidemiologic context: 1
- Linkage to confirmed pertussis case, severe paroxysms, whooping sound, or post-tussive vomiting suggests Bordetella pertussis infection
- Outbreaks in military personnel or college students may suggest Mycoplasma pneumoniae or Chlamydophila pneumoniae infection
When Cough Persists Beyond 3 Weeks
If cough persists for >3 weeks, acute bronchitis is no longer the diagnosis—consider: 1, 2
- Post-infectious cough
- Upper airway cough syndrome (postnasal drip)
- Asthma
- Gastroesophageal reflux disease
Diagnosing Chronic Bronchitis
Chronic bronchitis is diagnosed when a patient has chronic cough and sputum production occurring on most days for at least 3 months per year for 2 consecutive years, after excluding other respiratory or cardiac causes. 2, 3
Diagnostic Criteria for Chronic Bronchitis
- Chronic cough and sputum expectoration on most days for at least 3 months 2
- Symptoms present for at least 2 consecutive years 2
- Other respiratory or cardiac causes of chronic productive cough must be ruled out 2
Essential History
Obtain complete exposure history: 3
- Cigarette, cigar, and pipe smoking (responsible for 85-90% of cases) 3
- Passive smoke exposure 2, 3
- Occupational and home environmental hazards 2, 3
Critical Pitfall
Overdiagnosis of chronic bronchitis is extremely common—88.4% of patients with self-reported or physician-confirmed diagnoses do not actually meet standard criteria. 2