Description

• The spectrum of croup includes laryngotracheitis (LT), laryngotracheobronchitis (LTB), and laryngotracheobronchopneumonitis. It is often a result of a viral infection and most common cause of airway obstruction in young children.
• May occur in absence of viral prodrome, known as spasmodic croup, occurring in older children; rapid onset and resolution and often has a recurrent course

Epidemiology

• Most commonly affects children aged 6 months to 3 years of age, peaks at 18 months; although rare, croup can affect children as young as 3 months and as old as 6 to 7 years.
• Predominant sex: male > female
• Most often occurs in the fall and early winter but may present year-round

Incidence

• Accounts for 1.3% of emergency department cases
• The vast majority are considered mild cases, but 3–7% of cases require hospitalization.
• <3% require laryngoscopic or airway procedures.
• 4.4% of children returned to the emergency department within 48 hours (1).

Prevalence
60% of barking cough are resolved within 48 hours, and only 2% have symptoms persisting for >5 nights (1).

Etiology and Pathophysiology

• Infection of the larynx, trachea, and bronchi, causing narrowing of the airway secondary to inflammation and edema
• Children have narrow airway, and negative-pressure inspiration pulls airway walls closer together, creating inspiratory stridor.
• Typically, caused by viruses that infect oropharyngeal mucosa and migrates inferiorly; most common pathogen is parainfluenza virus, responsible for >80% of cases
  • Types 1 and 2 are the most common.
  • Type 3 is affiliated with bronchiolitis and pneumonia in young infants and children.
  • Type 4 (subtypes 4A and 4B) are associated with milder illness.
• Other viruses: RSV, paramyxovirus, influenza virus type A or B, adenovirus, rhinovirus, enteroviruses (coxsackie and echo), reovirus, measles virus where vaccination is not common, and metapneumovirus
• Mycoplasma pneumoniae and Corynebacterium diphtheriae have been reported but are rare.
• Bacterial croup is commonly caused by Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
• Spasmodic croup cause is unclear, possibly allergy, airway hyperactivity, and gastroesophageal reflux.

Genetics
Congenital subglottic stenosis, which is a narrowing of the lumen of the cricoid region, can present as recurrent croup.

Risk Factors

Prior intubations, structural airway abnormality, prematurity, and age <3 years increase the risks for recurrent croup (more than two episodes per year) (2).

General Prevention

Croup spreads through droplets. Children should be considered contagious up to 3 days after the start of illness and/or until afebrile. There is no specific vaccine for croup, but seasonal influenza vaccine may contribute to decreased risk.

Commonly Associated Conditions

• Some evidence suggests croup hospitalization may be associated with future development of asthma.
• If recurrent (more than two episodes in a year) or during the first 90 days of life, consider host factors or allergic factors.
• Underlying anatomic abnormality (e.g., subglottic stenosis, paradoxical vocal cord dysfunction)
• Consider gastroesophageal reflux disease diagnostic consideration for patients with recurrent croup symptoms.
• COVID-19—a potential viral agent in patients with croup