Croup

Definition

Croup, also known as laryngotracheobronchitis, is an acute viral infection of the upper airway in children, characterized by inflammation and narrowing of the larynx, trachea, and bronchi, leading to a distinctive barking cough, hoarseness, and stridor.

Epidemiology

• Commonly affects children aged 6 months to 3 years
• Peak incidence in fall and early winter
• Boys are slightly more affected than girls
• Most cases are mild and self-limited, but severe cases may require hospitalization
• Accounts for 15–20% of pediatric emergency visits for respiratory symptoms in the affected age group

Etiology

• Viral infection (most commonly parainfluenza virus types 1 and 3)
• Other viruses: RSV, adenovirus, influenza, metapneumovirus
• Rarely bacterial superinfection can complicate viral croup
• Family or daycare exposure increases risk
• History of previous croup episodes may predispose to recurrence

Pathophysiology

• Viral infection causes inflammation and edema of the larynx, subglottic region, and trachea
• Subglottic narrowing leads to turbulent airflow, producing stridor
• Inflammation of vocal cords causes hoarseness
• Airway obstruction can be dynamic and worsen during agitation or at night
• Severe edema may result in hypoxia and respiratory distress
• Secondary bacterial infection is rare but can exacerbate obstruction