Risk Factors
Age: 6 months to 6 years (peak 1–2 years)
Season: Autumn and early winter (April–June in Australia)
Viral illness exposure (siblings, childcare)
Previous history of croup
Underlying airway abnormalities (e.g. subglottic stenosis – more severe/recurrent)
Aetiology
Viral infection causing inflammation of larynx, trachea, and bronchi
Most common virus
Parainfluenza virus type 1 (esp. in epidemics)
Others: RSV, influenza A/B, adenovirus, rhinovirus
Viral replication → subglottic oedema → airway narrowing → inspiratory obstruction
Pathophysiology
Subglottic region = narrowest part of the upper airway in young children
Oedema causes inspiratory airflow limitation
Leads to:
Stridor (inspiratory, ± expiratory in severe cases)
Barking cough (seal-like)
± respiratory distress (sternal/intercostal recession, tracheal tug)
Crying/agitation worsens stridor due to increased airflow demands
Diagnosis
Clinical diagnosis – no labs or imaging usually required
Key features:
Barking cough
Inspiratory stridor (worse at night)
Hoarse voice
Low-grade fever
± Respiratory distress (recession, tachypnoea, agitation)
Symptoms often worse at night, peak over 1–2 days, resolve in ~3–4 days
Alert, not toxic appearing
Differential Diagnosis
Epiglottitis – drooling, muffled voice, toxic, abrupt onset
Bacterial tracheitis – high fever, toxic, purulent secretions
Foreign body aspiration – sudden onset, asymmetry on auscultation
Peritonsillar abscess – older child, trismus, muffled voice
Retropharyngeal abscess – neck stiffness, dysphagia, drooling
Anaphylaxis – rapid onset swelling, urticaria, hypotension
Investigations
Clinical diagnosis – no investigations needed in typical cases
If atypical or severe:
Neck X-ray: "Steeple sign" (subglottic narrowing)
Lateral neck X-ray: to rule out epiglottitis if uncertain
Viral swabs: not routinely necessary
Avoid agitating child for bloods/imaging if not necessary
Management
General principles
Keep child calm – crying worsens symptoms
Single dose of oral dexamethasone (0.15–0.6 mg/kg; RCH uses 0.15 mg/kg PO or IV)
Reduces severity, improves sleep, shortens illness
Use even in mild cases
Monitor for stridor at rest, work of breathing, air entry
Moderate–Severe croup
Add nebulised adrenaline (epinephrine): 5 mL of 1:1000 via nebuliser
Rapid temporary improvement (~2 hrs)
Use if: stridor at rest, distress, poor feeding, or hypoxia
Observe for 2–4 hours post-adrenaline for rebound symptoms
Oxygen if SpO₂ < 92%
Keep NBM if severe distress – risk of aspiration
Admission criteria (RCH / local guidelines)
Stridor at rest after steroid + adrenaline
Persistent respiratory distress or hypoxia
Poor oral intake or dehydration
Age <6 months
Concern for alternative diagnosis
Poor social supports or access to care
Complications & Prognosis
Rare in most mild-moderate cases
Severe airway obstruction
Hypoxia
Secondary bacterial tracheitis
Hospitalisation or ICU – for repeated adrenaline doses or respiratory failure
Generally excellent prognosis
Symptoms peak at 1–2 days, resolve by day 3–4
<5% require hospital admission
Recurrence common in some children (up to 10–15%)
No long-term complications in most cases