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Croup (acute laryngotracheobronchitis) is a respiratory illness of childhood and one of the most common causes of upper airway obstruction in children. Physicians should be comfortable with the disease as it will be one of the most frequent presentations of acute stridor in children to the office or emergency setting. In the United States, it is estimated to affect around 3% of the population and is most common in children aged 6 months to 6 years with the largest number of cases seen in those between 1 and 2 years of age.1 Reinfection and recurrence of croup is common. The ratio of males to females with croup is 1.43:1.1 There are two seasonal peaks of croup in North America, the first in autumn and the second in late winter.1 Because of biennial increases in viral epidemics, the number of croup cases is 50% higher in odd-numbered years when compared to even-numbered years.2

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Clinical symptoms of croup include a hoarse voice, a seal-like barky cough and stridor. As croup symptoms worsen, respiratory distress and occasionally cyanosis can appear. Symptoms typically worsen when the child is agitated and at nighttime. Fortunately croup symptoms are short-lived with the majority (60%) having resolution within 48 hours,3 and only a small portion having symptoms lasting up to 1 week.3 The majority of children with croup can be managed as outpatients with less than 5% requiring admission.46 For those children requiring hospitalization, the need for endotracheal intubation is rare (1–5%)7 and mortality is extremely rare.7,8

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Localized inflammation of the upper airway caused by an upper respiratory tract infection leads to varying degrees of airway obstruction and the range of symptoms seen in croup. Specifically, the infection causes the mucosa of the vocal folds and subglottis become erythematous and swollen.9 The subglottic area is the narrowest part of the airway and any edema affects the lumen negatively. This narrowing disrupts airflow resulting in the barky seal-like cough, stridor and increased work of breathing (indrawing).

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The most common viral etiologic agents for croup are parainfluenza viruses types 1 and 3. One study showed they were responsible for greater than 65% of the cases of croup.1 Most recently, human metapneumovirus has been identified as another etiologic agent for croup.10

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Table 31–1 lists the most common infectious and noninfectious causes of croup.

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Table 31–1. Etiologic Agents of Croup

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