Chapter 34: Croup

DEFINITIONS AND EPIDEMIOLOGY

Croup (acute laryngotracheobronchitis) is a respiratory illness of childhood and one of the most common causes of acute stridor in children seen in the office or emergency setting. In North America, croup affects approximately 3% of the population; it is most common in children aged 6 months–6 years, with the largest number of cases occurring in children 1–2 years of age.^1,2 The male : female ratio for croup is 1.4 : 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 with even-numbered years.³

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%) resolving within 48 hours,⁴ and only a small portion having symptoms lasting up to 1 week.⁴ Up to 5% of children with croup will have a repeat visit to a healthcare professional within one week of presentation.² The majority of children with croup can be managed as outpatients with less than 5% requiring admission.^5–7 For those children requiring hospitalization, the need for endotracheal intubation is rare (1–5%)⁷ and mortality is extremely rare.^8,9

PATHOGENESIS

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 to become erythematous and swollen.¹⁰ In children, 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).

The most common viral etiologic agents for croup are parainfluenza viruses types 1 and 3.¹ Recent studies using sensitive polymerase chain reaction (PCR)-based assays have identified a wide range of viruses as etiologic agents for croup, including human metapneumovirus, influenza A and B virus, rhinovirus, coronavirus, enterovirus, and adenovirus.^1,11–13 Table 34-1 lists the most common infectious causes of croup.