What are the onset and symptoms of croup?

Croup: Onset and Clinical Presentation

Onset Characteristics

Croup typically presents with sudden onset of distinctive respiratory symptoms, most commonly beginning with mild upper respiratory tract symptoms followed by the characteristic barking cough. 1, 2, 3

• The disease usually starts with low-grade fever and coryza (runny nose), mimicking a common cold 4
• This prodromal phase is then followed by the sudden appearance of the characteristic barking cough, often described as a "barking seal" sound 2, 3, 5
• The incubation and progression from initial symptoms to full croup manifestation occurs rapidly, often within 12-48 hours 4
• Symptoms typically occur without antecedent prolonged cough or significant congestion, distinguishing it from other respiratory illnesses 1

Cardinal Symptoms

The classic triad of croup symptoms includes:

Primary Respiratory Features

• Barking cough - the hallmark symptom, distinctive and seal-like in quality 2, 3, 5, 4
• Inspiratory stridor - a harsh, high-pitched sound during inspiration caused by upper airway narrowing 2, 3, 5
• Hoarse voice or cry - resulting from laryngeal inflammation 2, 3, 4

Associated Symptoms

• Respiratory distress with varying degrees of severity, including use of accessory muscles and chest retractions 1, 2, 3
• Low-grade fever is common, though high fever (>39°C) should raise concern for alternative diagnoses like bacterial tracheitis 6, 4
• Stridor at rest indicates moderate to severe disease requiring more aggressive intervention 1, 5

Severity Indicators

Mild Croup

• Barking cough without stridor at rest 7
• Minimal respiratory distress 7
• Normal oxygen saturation 1

Moderate to Severe Croup

• Stridor at rest 7, 1
• Increased respiratory rate (>70 breaths/min is concerning, especially in infants) 7, 1
• Use of accessory muscles and chest retractions 1, 5
• Agitation (may indicate hypoxia) 1

Life-Threatening Signs

• Silent chest (absence of breath sounds despite respiratory effort) 1
• Cyanosis 1, 5
• Fatigue or exhaustion 1, 5
• Oxygen saturation <92-94% despite oxygen therapy 7, 6

Clinical Course and Timeline

• Most symptoms resolve quickly, with the cough typically subsiding within 2 days in uncomplicated cases 4
• Symptoms are often worse at night 1
• The disease predominantly affects children aged 6 months to 3 years, with peak incidence around 2 years of age 4
• Age <18 months is a risk factor for more severe disease and hospitalization 7, 1

Important Clinical Pitfalls

Do not confuse croup with bacterial tracheitis, which presents with toxic appearance, high fever, progressive respiratory distress despite standard treatment, and purulent secretions 6. Foreign body aspiration can mimic croup but typically has sudden onset without fever or preceding upper respiratory symptoms 1, 6. The absence of the typical prodromal phase (coryza and low-grade fever) should prompt consideration of alternative diagnoses 1, 4.