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- Croup is a subacute viral illness characterized by upper airway symptoms such as seal-like barking cough, inspiratory stridor, and fever. “Croup” is used to refer to viral laryngotracheitis or laryngotracheobronchitis (LTB). It is sometimes used for LTB with pneumonitis, bacterial tracheitis, or spasmodic croup.
- Most common cause of upper airway obstruction or stridor in children
- Spasmodic croup: noninfectious form with sudden resolution
- No fever or radiographic changes
- Initially treated as croup
- Usually self-limiting and resolves with mist therapy at home
- Often recurs on same night or in 2 to 3 nights
- System(s) affected: respiratory
- Synonym(s): infectious croup; viral croup
- Predominant age
- Common among children 6 months to 3 years
- Most common during the 2nd year of life
- Rare among those <3 months and >6 years
- Predominant sex: male > female (1.5:1)
- Possible during any time of year but is most common in autumn and winter (with parainfluenza 1 and respiratory syncytial virus [RSV])
- Six cases per year per 100 children <6 years old
- 1.5–6% of cases require hospitalization.
- 2–6% of those require intubation.
- Decreasing incidence in the United States and Canada
Etiology and Pathophysiology
- Subglottic region/larynx is entirely encircled by the cricoid cartilage.
- Inflammatory edema and subglottic mucus production decrease airway radius.
- Small children have small airways with more compliant walls.
- Negative-pressure inspiration pulls airway walls closer together.
- The anatomically small airway is more susceptible to compromise and narrowing caused by the combined edema, mucus secretions, and increased compliance. Small decrease in airway radius causes significant increase in resistance (Poiseuille law: resistance proportional to 1/radius4).
- Typically caused by viruses that initially infect oropharyngeal mucosa and then migrate inferiorly
- Parainfluenza virus
- Most common pathogen: 75% of cases
- Type 1 is the most common, causing 18% of all cases of croup.
- Types 2, 3, and 4 are also common.
- Type 3 may cause a particularly severe illness.
- Other viruses: RSV, paramyxovirus, influenza virus type A or B, adenovirus, rhinovirus, enteroviruses (coxsackie and echo), reovirus, measles virus where vaccination not common, and metapneumovirus
- Haemophilus influenzae type B now rare with routine immunization
- May have bacterial cause: Mycoplasma pneumoniae has been reported.
- Age group 2 to 3 years, with range of 6 months to 6 years
- Seasonality: fall and winter
- Epidemic outbreaks with associated URI symptoms
Seasonal influenza shots may decrease risk.
Commonly Associated Conditions
- If recurrent (>2 episodes in a year) or during first 90 days of life, consider host factors.
- Underlying anatomic abnormality (e.g., subglottic stenosis)
- In one study, found to be present in 59% children with recurrent croup
- Paradoxical vocal cord dysfunction
- Gastroesophageal reflux disease
- Neonatal intubation