About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Most common LRTI in infants — peak at 3–6 months, rare after 12 months
- Caused by RSV (~80%), also rhinovirus, parainfluenza, metapneumovirus
- Clinical diagnosis: coryzal prodrome then cough, tachypnoea, feeding difficulty, wheeze/crackles
- Management is SUPPORTIVE ONLY: oxygen if SpO2 <92%, NG/IV fluids if poor feeding, suction for nasal secretions
- DO NOT give bronchodilators, steroids, or antibiotics — they are NOT effective and not recommended by NICE
- Admission criteria: SpO2 <92%, taking <50% usual feeds, respiratory distress, apnoea, age <6 weeks or premature
Overview
Bronchiolitis is an acute viral infection of the lower respiratory tract affecting the bronchioles. It is the most common reason for hospital admission in infants during winter months. RSV accounts for approximately 80% of cases. The pathology involves inflammation, oedema, and necrosis of the bronchiolar epithelium with mucus plugging, leading to small airway obstruction. The disease is self-limiting in the vast majority, with supportive care being the mainstay of treatment.
Epidemiology
Bronchiolitis affects approximately 30% of infants in their first year of life, with 2–3% requiring hospital admission. Peak incidence is at 3–6 months. It is seasonal — predominantly October to March in the UK. Risk factors for severe disease include prematurity, age <6 weeks, congenital heart disease, chronic lung disease (BPD), immunodeficiency, and Down syndrome. Almost all children have had RSV infection by age 2.
Clinical Features
Symptoms
Coryzal prodrome (1–3 days): runny nose, sneezing, mild cough, low-grade fever
Cough — initially dry, may become wet
Feeding difficulty — most important symptom to assess (poor intake = marker of severity)
Irritability and increased work of breathing
Apnoeic episodes (especially in young or premature infants)
Signs
Tachypnoea (increased respiratory rate for age)
Subcostal and intercostal recession, nasal flaring
Fine inspiratory crackles on auscultation (hallmark finding)
Expiratory wheeze (less prominent than crackles)
Hyperinflation of the chest
SpO2 <92% in air
Grunting (sign of severe respiratory distress)
Head bobbing, see-saw breathing (severe)
Investigations
First-line
Clinical diagnosisDiagnosis is CLINICAL — no routine investigations needed in straightforward bronchiolitis
Pulse oximetrySpO2 monitoring — <92% requires oxygen supplementation and is an admission criterion
Second-line
Nasopharyngeal aspirate (NPA)RSV rapid antigen test or PCR — for infection control (cohorting on ward), not for diagnosis
CXRNOT routine — only if diagnostic uncertainty (e.g. suspected pneumonia, foreign body) or deteriorating despite appropriate care
Blood gasOnly in severe disease or if considering ventilatory support — assess for hypercarbia
Specialist
Further investigationRarely needed — consider if atypical presentation, recurrent episodes, or underlying condition suspected
1
Supportive care — the ONLY treatment
- Oxygen if SpO2 persistently <92% — nasal cannulae or HFNC
- Feeding support: small frequent feeds; NG tube feeds if <50% usual intake; IV fluids if unable to tolerate NG
- Nasal suctioning: gentle nasal suction before feeds if copious secretions
- Monitoring: SpO2, respiratory rate, feeding, urine output, apnoea episodes
2
What NOT to give (NICE explicitly states DO NOT use)
- Do NOT give bronchodilators (salbutamol)
- Do NOT give systemic or inhaled corticosteroids
- Do NOT give antibiotics (unless confirmed secondary bacterial infection)
- Do NOT give hypertonic saline nebulisers
- Do NOT perform CXR or blood tests routinely
3
Admission criteria
- SpO2 <92% in air
- Taking <50% of usual fluid intake
- Severe respiratory distress
- Apnoea (observed or reported)
- Age <6 weeks or ex-premature
- Significant comorbidity (CHD, chronic lung disease, immunodeficiency)
4
Escalation and discharge
- HFNC or CPAP if worsening despite supplemental oxygen
- Intubation and ventilation for severe respiratory failure or recurrent apnoea
- Discharge when SpO2 >92% for 4+ hours including sleep, feeding 75%+ usual, no distress
- Advise parents: symptoms peak day 3–5, cough may persist 3 weeks
Complications
- Respiratory failure: May require HFNC, CPAP, or intubation in 2–3% of admitted infants
- Apnoea: Especially concerning in young or premature infants
- Dehydration: From poor feeding
- Secondary bacterial infection: Rare — consider if fever persists beyond 72 h
- Post-bronchiolitis wheeze: ~30% develop episodic wheeze in early childhood
UKMLA Exam Tips
- 1Bronchiolitis is a CLINICAL diagnosis — do NOT order CXR or blood tests routinely
- 2Treatment is SUPPORTIVE ONLY. Salbutamol and steroids DO NOT WORK — classic exam trap
- 3RSV is the cause in ~80%. Peak age 3–6 months. Season: winter (Oct–Mar)
- 4Fine inspiratory crackles (not wheeze) are the hallmark auscultatory finding
- 5Admission if SpO2 <92%, feeding <50%, severe distress, apnoea, age <6 weeks, significant comorbidity
- 6Palivizumab is given prophylactically to high-risk infants — NOT a treatment
practicetest your knowledge on bronchiolitisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — paediatrics and beyond.
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