What differentiates an upper respiratory infection (URI) from bronchiolitis in terms of clinical presentation and treatment?

Differentiating Upper Respiratory Infection from Bronchiolitis

Bronchiolitis is distinguished from an upper respiratory infection (URI) by the presence of lower respiratory tract signs—specifically tachypnea, wheezing, rales, and increased respiratory effort (retractions, nasal flaring, grunting)—that follow an initial viral upper respiratory prodrome in children under 2 years of age. 1, 2, 3

Clinical Presentation Pattern

Upper Respiratory Infection Features

• Isolated upper airway symptoms: rhinorrhea, congestion, sneezing, cough, and possibly fever without progression to lower respiratory involvement 4, 5
• No increased work of breathing: absence of tachypnea, retractions, or accessory muscle use 1
• Normal respiratory rate and effort 1

Bronchiolitis Features

Bronchiolitis presents in a characteristic two-phase pattern:

• Phase 1 (Days 1-4): Viral upper respiratory prodrome identical to URI—rhinorrhea, congestion, fever 1, 5
• Phase 2 (Following prodrome): Progression to lower respiratory tract involvement with:
  • Tachypnea (respiratory rate ≥70 breaths/minute indicates increased severity risk) 1, 3
  • Wheezing and/or rales on auscultation 1, 2
  • Increased respiratory effort: grunting, nasal flaring, intercostal/subcostal retractions 1, 3
  • Difficulty feeding due to respiratory distress 1, 6

Key Diagnostic Algorithm

The diagnosis of bronchiolitis is clinical and requires all three elements:

1. Child under 2 years of age 1, 2, 3
2. Viral upper respiratory prodrome 1, 3
3. Lower respiratory signs (wheezing, rales, tachypnea) with increased respiratory effort 1, 3

If only upper respiratory symptoms are present without lower respiratory tract involvement, the diagnosis is URI, not bronchiolitis. 1

Assessment of Disease Severity

When bronchiolitis is diagnosed, assess for high-risk features:

• Age <12 weeks (particularly <6 weeks) 1, 3
• History of prematurity (<37 weeks gestation) 1, 3
• Hemodynamically significant congenital heart disease 1, 3
• Chronic lung disease (bronchopulmonary dysplasia) 1, 3
• Immunodeficiency 1, 3
• Apnea episodes (associated with severe disease) 1

Critical Physical Examination Points

Serial observations are essential, as bronchiolitis has significant temporal variability:

• Count respiratory rate for full 60 seconds (not estimated) 3
• Assess oxygen saturation: SpO₂ <94% is the best predictor of hospitalization; SpO₂ ≤97% predicts longer hospital stay 7
• Evaluate feeding ability and hydration status 1, 6, 3
• Assess mental status for lethargy or irritability 3

Upper airway obstruction from nasal congestion can contribute to work of breathing in bronchiolitis, so nasal suctioning before examination may affect assessment. 1

Diagnostic Testing

Routine laboratory studies, chest radiographs, and viral testing are NOT recommended for typical bronchiolitis, as they do not alter management and may lead to inappropriate antibiotic use. 1, 2, 3, 8

Chest radiography should be reserved for:

• Hospitalized children not improving at expected rate 1
• Severity requiring further evaluation 1
• Suspicion of alternative diagnosis 1

Treatment Implications

The distinction matters because treatment differs fundamentally:

URI Management

• Supportive care only 4
• Symptom relief measures 4

Bronchiolitis Management

• Supportive care: adequate oxygenation (maintain SpO₂ >90%) and hydration 2, 4, 5
• Avoid ineffective therapies: bronchodilators, corticosteroids, antibiotics, chest physiotherapy are NOT routinely recommended 2, 8, 4, 5
• Gentle nasal suctioning only when visible congestion affects breathing or feeding (avoid deep suctioning) 6
• Nasogastric or IV fluids if unable to maintain oral hydration 4, 5

Common Pitfall

The most common error is diagnosing bronchiolitis in a child with only upper respiratory symptoms. Without lower respiratory tract signs (wheezing, rales, tachypnea, increased work of breathing), the diagnosis remains URI regardless of the child's age or viral season. 1, 3