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- Croup is a subacute viral illness frequently preceded by 24 to 72 hours of symptoms such as nonspecific cough, coryza, rhinorrhea, fever with an abrupt onset of seal-like barking cough, and inspiratory stridor. Symptoms are worse at night and can rapidly fluctuate depending on whether the child is calm or agitated.
- The term croup is used to refer to viral laryngotracheitis or laryngotracheobronchitis (LTB). It is sometimes used for LTB with pneumonitis, bacterial tracheitis, or spasmodic croup.
- Spasmodic croup is a noninfectious form with sudden resolution that is usually self-limiting; it is treated like croup and resolves with mist therapy at home.
- Croup is the most common cause of upper airway obstruction or stridor in children.
- Predominant age
- Ranges from 6 months to 6 years
- Most commonly seen in children among 6 months to 3 years with a peak around the 2nd year of life
- Predominant sex: male > female (1.5:1)
- Possible during any time of year but is most common during the fall and winter
- Human parainfluenza 1 and respiratory syncytial virus (RSV) are the most common viral causes.
- Six cases per year per 100 children <6 years old
- 1.5–6% of cases require hospitalization.
- 2–6% of those require intubation. 60% of barking cough resolved within 48 hours, and only 2% have symptoms persisting for longer than 5 nights.
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.
There is not a specific vaccine for croup, but seasonal influenza shots may contribute to decreased 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% of children with recurrent croup
- Paradoxical vocal cord dysfunction
- Gastroesophageal reflux disease
- Neonatal intubation