What Causes Croup in Children
Parainfluenza viruses are the primary cause of croup, with types 1 and 2 being most commonly responsible for the syndrome. 1
Primary Viral Etiology
Parainfluenza viruses account for the majority of croup cases and are responsible for up to 11% of all hospitalizations in children under 5 years of age. 1 These viruses are the dominant pathogen across multiple studies examining croup etiology. 2, 3, 4
Other Viral Causes
While parainfluenza is predominant, several other viruses can cause croup, including: 1
- Respiratory syncytial virus (RSV)
- Rhinoviruses
- Human coronaviruses
- Adenoviruses
- Influenza viruses
- Human metapneumovirus
Important Clinical Distinction
Influenza-associated croup tends to be more severe than parainfluenza-associated croup and carries a higher risk of progression to bacterial tracheitis as a complication. 1, 5 This is a critical pitfall to recognize when evaluating children with more severe presentations.
Pathophysiology
The viral infection causes varying degrees of epithelial destruction, but all causative viruses produce vasodilation and hypersecretion in the upper airway. 1 This inflammatory response leads to the characteristic laryngeal and tracheal swelling that produces the barking cough, inspiratory stridor, and hoarseness seen in croup. 2, 3
Age-Related Considerations
Croup primarily affects children 6 months to 6 years of age, with peak incidence between 6 months and 3 years. 3, 6 The condition accounts for up to 15% of emergency department visits for respiratory disease in this age group. 2
Prevention Limitations
No vaccine exists for parainfluenza viruses, which are the primary cause of croup. 1 While annual influenza vaccination is recommended for all children ≥6 months of age and can prevent influenza-associated croup, it does not protect against parainfluenza viruses. 1 Standard childhood immunizations protect against bacterial pathogens like Streptococcus pneumoniae, Haemophilus influenzae type b, and pertussis, but these are not primary causes of croup. 1