Croup is a self-limited upper respiratory infection causing inflammation of the larynx and subglottic airway that presents with barking cough and inspiratory stridor. Although usually mild, croup can cause significant respiratory distress and even death.
- Croup refers to as viral laryngotracheitis (LT) or laryngotracheobronchitis (LTB). It is a common viral illness presenting with nonspecific upper respiratory symptoms.
- Croup causes upper airway inflammation and obstruction leading to pathognomonic barking cough and inspiratory stridor; symptoms start abruptly and are worse at nighttime.
- Most commonly affects children aged 6 months to 3 years of age, with average affected age around 2.5 years old. 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 last fall and early winter, but may present year-round
- Accounts for 1.3% of emergency department cases
- The vast majority are considered mild cases, but 3–7% of cases require hospitalization.
- Less than 3% require laryngoscopic or airway procedures.
- 4.4% of children returned to the emergency department within 48 hours (1).
60% of barking cough resolved within 48 hours and only 2% have symptoms persisting for longer than 5 nights (1).
Etiology and Pathophysiology
- Infection of the larynx and subglottic region, causing narrowing of the airway secondary to inflammation and edema
- Small children have narrow airway enabling greater ease of edema collection. Negative-pressure inspiration pulls airway walls closer together, creating inspiratory stridor.
- Typically, caused by viruses that initially infect oropharyngeal mucosa and migrates inferiorly, most common pathogen being parainfluenza virus (types 1 to 4), responsible for over 80% of cases
- Type 1 is the most common.
- Type 3 is affiliated with bronchiolitis and pneumonia in young infants and children.
- Type 4, further categorized into subtypes 4A and 4B, is not well understood but is associated with a 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.
Congenital subglottic stenosis, which is a narrowing of the lumen of the cricoid region, can present as recurrent croup.
Prior intubations, prematurity, and age <3 years increase the risks for recurrent croup (more than two episodes per year) (2).
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 decrease risk.
Commonly Associated Conditions
- Some evidence suggests croup hospitalization may be associated with future development of asthma.
- If recurrent (>2 episodes in a year) or during 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.
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