How do I differentiate and treat bronchitis versus pneumonia based on symptoms?

Differentiating Bronchitis from Pneumonia Based on Symptoms

Pneumonia should be suspected when a patient presents with acute cough PLUS at least one of the following: new focal chest signs (rales, egophony, fremitus), dyspnea, tachypnea, or fever lasting more than 4 days—and when these findings are present, chest radiography should be performed to confirm the diagnosis. 1

Key Clinical Features That Distinguish Pneumonia from Bronchitis

Vital Sign Abnormalities Strongly Suggest Pneumonia

The absence of ALL of the following vital sign abnormalities substantially reduces the likelihood of pneumonia to the point where bronchitis is more likely and further diagnostic testing may be unnecessary: 1, 2

• Heart rate ≥100 beats/min 1, 3
• Respiratory rate ≥24 breaths/min 1, 3
• Oral temperature ≥38°C (100.4°F) 1, 3

If all three vital signs are normal, pneumonia is unlikely (reduced to approximately 2% probability from baseline 5-10%). 1

Physical Examination Findings That Favor Pneumonia Over Bronchitis

Focal chest signs are the most diagnostically significant findings: 3

• New and localizing crackles (rales) are highly suggestive of pneumonia 3, 2
• Egophony or increased fremitus indicate consolidation and pneumonia 1, 3
• Diminished breath sounds in a localized area suggest pneumonia 3
• Dull percussion note or pleural rub (when present, make pneumonia very likely, though these are uncommon) 1

In contrast, bronchitis typically presents with diffuse wheezing or rhonchi without focal findings. 1

Symptom Patterns That Differentiate the Two Conditions

Symptoms favoring pneumonia: 1, 4

• Dyspnea and tachypnea are prominent features 1, 3
• Pleuritic chest pain (sharp, worse with breathing) 4
• High fever with chills and rigors 5
• Fever persisting >4 days 1, 6
• Absence of upper respiratory symptoms (no runny nose, sore throat) increases pneumonia likelihood 1, 3

Symptoms favoring bronchitis: 1

• Cough as the predominant symptom with accompanying upper respiratory features 1
• Sore throat or rhinorrhea suggest upper respiratory infection/bronchitis 1
• Normal vital signs throughout the illness 1
• Symptoms lasting <3 weeks (acute bronchitis definition) 1

Critical Pitfall: Purulent Sputum Does NOT Distinguish Between Conditions

A common misconception is that purulent (green/yellow) sputum indicates bacterial pneumonia requiring antibiotics. Purulence occurs when inflammatory cells or sloughed epithelial cells are present and can result from either viral or bacterial infection—it does NOT reliably distinguish pneumonia from bronchitis. 1 The absence of purulent sputum also does not rule out bacterial infection. 1

Laboratory Testing to Support the Diagnosis

C-Reactive Protein (CRP) Can Help When Clinical Picture Is Unclear

• CRP >100 mg/L makes pneumonia more probable 3, 6
• CRP <20 mg/L with symptoms >24 hours makes pneumonia very unlikely 3, 6
• CRP 11-50 mg/L without dyspnea and daily fever effectively rules out pneumonia 3, 7

A decision rule validated in primary care found that patients with CRP <10 μg/ml can have pneumonia ruled out, potentially reducing unnecessary antibiotic prescriptions by 9.1%. 7

Chest Radiography: When to Order

Indications for Chest X-ray (Suspecting Pneumonia)

Order chest radiography when: 6

• Age ≥60 years (especially with comorbidities) 6
• Any vital sign abnormality (HR >100, RR >24, temp ≥38°C) 6
• New focal chest signs on examination 1, 6
• Dyspnea or tachypnea 1, 6
• Fever >4 days 1, 6
• CRP >100 mg/L 6
• Hemoptysis 6
• Cough persisting >3 weeks 6

When Chest X-ray Is Unnecessary (Bronchitis More Likely)

Chest radiography can be safely avoided when: 6

• All vital signs are normal 6
• Normal pulmonary auscultation (no focal findings) 6
• CRP <20 mg/L with symptoms >24 hours 6
• Healthy adults <40 years without vital sign abnormalities or asymmetric lung sounds (pneumonia rate only 4%) 6

Treatment Implications Based on Diagnosis

For Bronchitis (No Pneumonia Suspected)

When vital signs and lung examination are normal, routine antibiotics are NOT recommended. 3 A large placebo-controlled trial of 2,061 patients with acute lower respiratory tract infection (where pneumonia was not suspected) found that amoxicillin provided minimal benefit—duration of moderately bad symptoms was identical between groups, and antibiotics caused more adverse effects (nausea, rash, diarrhea). 8 This held true even in patients ≥60 years old. 8

For Pneumonia (Confirmed or Highly Suspected)

Empiric antibiotics should be initiated immediately according to local guidelines when pneumonia is suspected, even if imaging cannot be obtained. 3 Delayed appropriate antimicrobial therapy increases mortality. 9

Special Considerations in High-Risk Populations

Elderly Patients (≥60 Years)

Maintain a high index of suspicion for pneumonia in elderly patients, as they present with fewer typical respiratory symptoms. 3, 9 They may present with: 1

• Confusion or altered mental status 1
• Failure to thrive 1
• Falls 1
• Worsening of underlying chronic illness 1
• Fever may be absent, but tachypnea is usually present 1

Use a lower threshold for chest radiography in this population due to higher pneumonia incidence, increased mortality risk, and atypical presentations. 6

When Chest X-ray Is Normal But Clinical Suspicion Remains High

A normal chest X-ray does not rule out pneumonia—radiographic changes may not be present early in the disease course or may be masked by dehydration. 3, 9 In these cases: 3

• Consider repeating chest radiograph in 24-48 hours as radiographic changes develop over time 3
• CT chest detects pneumonia in 27-33% of patients with negative chest X-rays and clinical suspicion 3
• Lung ultrasound has 93-96% sensitivity and specificity compared to chest radiograph 3
• Initiate empiric antibiotics if vital signs are abnormal, focal chest findings are present, and CRP >30 mg/L 3