How do you differentiate between viral upper respiratory tract infection, pneumonia, acute bronchitis, and asthma or Chronic Obstructive Pulmonary Disease (COPD) exacerbation?

Distinguishing Respiratory Conditions: A Clinical Algorithm

The key to differentiation lies in identifying focal chest signs, fever patterns, wheezing characteristics, and smoking history—with chest radiography reserved for suspected pneumonia based on specific clinical triggers. 1

Step 1: Rule Out Pneumonia First (Highest Mortality Risk)

Pneumonia must be distinguished from other conditions because it carries higher mortality and requires different management. 1

Suspect pneumonia when ANY of the following are present:

• New focal chest signs on auscultation (39% probability vs. 5-10% baseline) 1
• Dyspnea or tachypnea 1
• Pulse rate >100 bpm 1
• Fever persisting >4 days 1
• Dull percussion note or pleural rub (highly specific when present) 1

Use C-Reactive Protein (CRP) to refine suspicion:

• **CRP <20 mg/L** (with symptoms >24 hours): pneumonia highly unlikely 1
• CRP >100 mg/L: pneumonia likely 1
• Chest X-ray is the gold standard and should be performed when clinical suspicion persists after CRP testing 1

Critical pitfall: Absence of focal signs reduces pneumonia probability to only 2%, but does not exclude it entirely. 1

Step 2: Differentiate Viral URTI from Lower Respiratory Tract Infections

Viral URTI characteristics:

• Predominantly upper respiratory symptoms (nasal congestion, sore throat, rhinorrhea) 1
• Cough may be present but is not the dominant symptom 1
• Absence of dyspnea 1
• Normal respiratory rate 1

Acute Bronchitis characteristics:

• Cough is the predominant symptom (with or without sputum) 1
• Absence of focal chest signs 1
• No dyspnea or tachypnea 1
• Fever typically <4 days 1

Important note: Differentiating between tracheitis and acute bronchitis is impossible and clinically irrelevant in practice—both are managed similarly. 1, 2

Step 3: Identify Asthma/COPD Exacerbation (Not Infection)

Up to 45% of patients presenting with acute cough >2 weeks actually have underlying asthma or COPD, not simple bronchitis. 1

Consider lung function testing when ≥2 of the following are present:

• Wheezing (as symptom or sign) 1
• Prolonged expiration 1
• Smoking history (especially in elderly patients) 1
• History of allergy 1
• Previous consultations for wheezing or cough 1
• Female sex (for asthma) 1

COPD/Asthma exacerbation must be differentiated from:

• Acute coronary syndrome (especially with cardiovascular disease history) 3
• Acute decompensated heart failure (presents identically with dyspnea) 3
• Pulmonary embolism (reduced mobility, recent hospitalization) 3
• Pneumonia (bacterial superinfection is common) 3

Key clinical features supporting true exacerbation:

• Increased dyspnea is the cardinal symptom 1, 3
• Increased sputum volume and purulence 1, 3
• Increased cough and wheeze 1

Step 4: Recognize Viral Triggers in Exacerbations

Viral infections commonly trigger both asthma and COPD exacerbations, but this does not exclude bacterial superinfection. 1, 4, 5

Viral detection patterns:

• Rhinovirus/enterovirus is most common (27.5-35.7% of exacerbations) 4, 6
• Influenza virus (22.5%) 6
• Respiratory syncytial virus (13.3%) 6
• Coronavirus (12.5-25.9%) 4, 6

Features suggesting viral infection in exacerbations:

• Symptoms of rhinopharyngitis (OR 1.98) 6
• Elevated CRP levels (OR 2.76) 6
• Low eosinophil count (OR 1.74) 6
• Inhaled corticosteroid use (OR 1.70) 6

Critical pitfall: Only 24% of patients with URTI-related exacerbations have the same virus detected at URTI onset and during exacerbation, indicating complex pathophysiology. 4

Step 5: Assess Complication Risk

High-risk features requiring close monitoring (age >65):

• Presence of COPD, diabetes, or heart failure 1
• Previous hospitalization in past year 1
• Oral glucocorticoid use 1
• Recent antibiotic use (previous month) 1
• General malaise 1
• Absence of upper respiratory symptoms (paradoxically suggests more severe disease) 1
• Confusion or diminished consciousness 1
• Vital sign abnormalities: pulse >100, temperature >38°C, respiratory rate >30, blood pressure <90/60 1

For patients <65 years:

• Diabetes and pneumonia diagnosis are primary risk factors 1
• Active malignancy, liver disease, renal disease, and immunocompromising conditions increase risk at all ages 1

Major pitfall to avoid: Do not assume all acute respiratory worsening in COPD patients represents exacerbation—comorbidities frequently cause identical symptoms and require different management. 3