Introduction
Croup_Disease Background 1
Croup is characterized as an acute, rapidly progressing respiratory disease resulting from the inflammation of the upper airway, larynx, and trachea. This is also referred to as laryngotracheitis, laryngotracheobronchitis, and laryngotracheobronchopneumonitis. Croup is often self-limiting and managed as outpatient, but may cause significant upper airway obstruction and respiratory distress that require evaluation and treatment in the emergency department. This develops concurrently with coryzal disease.
Epidemiology
Croup is one of the most common causes of acute respiratory distress in young children. This affects approximately 3% of children yearly, and is more common in children ≤6 years old, with peak incidence between 6 months to 3 years of age. This rarely occurs in adults. The condition demonstrates a higher prevalence in boys than in girls.
The epidemiologic patterns of croup vary significantly depending on region and climate. In the United States and Canada, hospitalizations increase during the autumn and early winter (September to December) of odd-numbered years. A prospective data from Finland indicate that admissions peak primarily in the late spring or autumn, while studies out of Korea show the highest incidence of croup was spring and winter.
Etiology
Croup_Disease Background 2
Croup is most commonly caused by parainfluenza virus 1-3, with type 1 being most common. Other respiratory viruses, such as rhinovirus, respiratory syncytial virus, and coronavirus disease 2019, may also trigger the development of croup.
Please see Respiratory Syncytial Virus and Coronavirus Disease 2019 (COVID-19) disease management chart for further information.
Pathophysiology
The viral infection leads to widespread airway inflammation and mucosal swelling across the larynx, trachea, and bronchi, followed by tissue cell death (necrosis) and increased secretions. The parainfluenza virus worsens the airway edema by stimulating chloride secretion and blocking sodium absorption in the tracheal epithelium.
Risk Factors
Croup_Disease Background 3
Risk factors for croup include family or previous history of croup; pre-existing narrowing of upper airways; conditions that cause reduced airway tone and predispose to respiratory failure (eg trisomy 21, neuromuscular conditions); and young age (uncommon in under 6 months old).