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Bronchiolitis in Paediatrics

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Definition

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Epidemiology

• Most common severe respiratory illness in infancy
• Seasonal: peaks November to April in temperate climates
• Nearly all children are infected at least once in their first 2 years of life
• Rarely fatal in otherwise healthy infants
• Accounts for large numbers of hospitalisations each winter

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Aetiology

Transmission: Fomites (hand-to-nose/eye) and respiratory droplets from coughing/sneezing. Viral shedding begins before symptom onset and continues for 2-3 weeks in immunocompetent infants. Incubation period: 2-8 days.

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Pathophysiology

1. Viral replication begins in upper airway epithelial cells
2. Spreads to mucosal surfaces of the lower respiratory tract
3. Infected epithelial cells are destroyed by lysis or apoptosis
4. Results in: epithelial cell necrosis + monocytic inflammation + peribronchial oedema + mucus and fibrin plugging of distal airways
5. Leads to: wheezing + lower airway obstruction
6. Air trapping + atelectasis → V/Q mismatch → hypoxaemia
7. Younger infants are at risk for fatigue → hypercarbia + respiratory failure

Key fact: Infants < 12 months have smaller calibre distal airways and lack active immunity to most respiratory viruses, making them prone to more severe disease. An infant < 12 months has an oxygen consumption index double that of an adult.

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Clinical Features

Presentation

• Typically < 12 months, winter presentation
• Prodrome (2-4 days): nasal congestion, copious rhinorrhoea
• Followed by: tight cough + difficulty feeding (± audible wheeze)
• Fever in ~one-third of admitted patients
• Very young infants: may present with apnoea (may precede respiratory symptoms)
• Parents may report poor feeding, decreased wet nappies

Examination Findings

• Tachycardia, tachypnoea, hypoxia, nasal flaring
• Intercostal/subcostal/substernal retractions
• Prolonged expiratory phase
• Diffuse wheeze (often with shifting crackles/rales)
• Decreased air entry in severe disease
• Irritability or lethargy = sign of severity
• Assess hydration: fontanel, mucous membranes, capillary refill, skin turgor

Severity Assessment (Bronchiolitis Assessment Tool)

Disease Course

• Worst in the first few days
• Median hospital stay: 2-3 days
• Entire illness duration: median 12 days
• Cough and noisy breathing can persist > 4 weeks

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Complications

• Acute bacterial otitis media (most common bacterial complication)
• Respiratory failure / apnoea
• Dehydration
• Pneumonia (secondary bacterial)
• Post-infectious wheezing / asthma (strong association between early RSV infection and subsequent asthma - though causality unclear)
• Bronchiolitis obliterans (rare, especially post-adenovirus)

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Risk Factors for Severe Disease

• Age < 3 months
• Prematurity / low birth weight
• Chronic lung disease (e.g. bronchopulmonary dysplasia)
• Congenital heart disease
• Immunodeficiency
• Neuromuscular disease

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Investigations

Bronchiolitis is a clinical diagnosis. Investigations have limited value and are not routinely recommended.

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Management

Principles

Supportive Care (mainstay)

• Oxygen supplementation for SaO₂ < 92% (or < 90-94% depending on guideline)
• Fluid support: IV/NG fluids if unable to tolerate oral feeds
• Nasal suction (gentle) to clear secretions, especially before feeds
• Upright positioning
• Monitoring (SpO₂, respiratory rate, feeding)

Pharmacological Therapies - NOT routinely recommended

Respiratory Support

• High-flow nasal cannula (HFNC): may help prevent need for intubation in moderate-severe disease; evidence is limited - reserve for moderate-to-severe cases
• CPAP: similarly, limited evidence; use in moderate-severe disease
• Mechanical ventilation: for respiratory failure; permissive hypercapnia strategy to minimise barotrauma

Criteria for Hospital Admission

• RR > 70 breaths/min
• SaO₂ ≤ 95%
• Age < 3 months
• Poor feeding / dehydration
• Significant retractions or accessory muscle use
• Apnoea
• Parental concern / inability to monitor at home
• High-risk comorbidities (CHD, CLD, prematurity)

Note: Temperature (fever) alone is NOT an indication for admission.

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Prevention

• Palivizumab (anti-RSV monoclonal antibody): monthly IM injections given prophylactically during RSV season to high-risk infants (premature, CHD, chronic lung disease). Not a treatment once infected.
• Nirsevimab: newer long-acting monoclonal antibody (single dose); increasingly used in many countries for broader RSV prophylaxis in infants
• Hand hygiene: most effective preventive measure; meticulous handwashing reduces fomite transmission
• Contact precautions in hospital (droplet + contact isolation)
• RSV vaccine: maternal RSV vaccines (e.g. Abrysvo) are now approved to protect newborns via passive immunity

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Differential Diagnosis

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Key Points to Remember

1. Clinical diagnosis - do not over-investigate
2. RSV causes ~70% of cases; peaks in winter
3. No pharmacological treatment consistently works - supportive care is the cornerstone
4. Corticosteroids and SABAs are not routinely indicated despite widespread prescribing
5. Fever alone does not indicate admission - look at respiratory rate, SpO₂, feeding, and age
6. Infants < 3 months and those with comorbidities are at highest risk
7. Apnoea can be the presenting feature in very young infants
8. Cough can persist > 4 weeks - reassure parents

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• A 2024 systematic review (PMID 38902454) confirms evidence-based supportive management remains the standard for high-risk infants in ICU settings, reinforcing avoidance of unproven therapies.
• A 2026 systematic review (PMID 41906981) on bronchiolitis investigations in infants supports the clinical guideline that routine investigations are not warranted.