Distinguishing Bacterial from Viral Cough

Introduction to Cough Diagnosis

The European Respiratory Society states that testing for specific pathogens is often not useful in daily practice, as most acute coughs are viral and self-limiting 1, 2
The American College of Physicians and Centers for Disease Control explicitly recommend against antibiotic use for acute bronchitis unless pneumonia is suspected, as antibiotics provide no benefit for viral bronchitis and contribute to antimicrobial resistance 3

Persistent fever with rigors may indicate pneumonia, which may require antibiotics 3
Tachypnea or increased respiratory rate, abnormal lung findings on examination, and hypoxemia are signs suggesting pneumonia 6
Age >75 years with fever, and presence of cardiac failure, insulin-dependent diabetes, or serious neurological disorder are also risk factors for pneumonia 4
If pneumonia is suspected, a chest radiograph is the gold standard for diagnosis 2, 6

Up to 45% of acute coughs lasting more than 2 weeks in COPD or asthma patients may represent exacerbations of underlying lung disease rather than a new infection 1, 2, 4
Wheezing, prolonged expiration, history of smoking, and symptoms of allergy are signs that may indicate underlying lung disease 1, 6

The American College of Physicians recommends against antibiotic use for uncomplicated acute cough, as antibiotics provide no benefit for viral bronchitis and contribute to antimicrobial resistance 3
Patients with COPD or asthma should focus on optimizing chronic disease management rather than seeking antibiotics for each cough episode 1, 2, 4

Patients should return for reassessment if cough persists beyond 3 weeks, new concerning symptoms develop, or symptoms worsen despite initial management 4, 5, 6
Alternative diagnoses to consider in these cases include pertussis, Mycoplasma/Chlamydophila pneumoniae, undiagnosed asthma or COPD, post-nasal drip, and gastroesophageal reflux 4, 5, 6