Last reviewed 12/2022

Croup is a generic term that covers a heterogeneous group of diseases that affects the larynx, trachea, and bronchi (1):
  • components of the croup syndrome include (1)
    • laryngotracheitis
    • laryngotracheobronchitis
    • laryngotracheobronchopneumonitis
    • spasmodic croup
  • some define croup as two types
    • infectious croup:
      • commonly caused by virus
        • viral croup
      • rarely caused by bacterium
        • Mycoplasma pneumoniae is a rare cause of mild croup in children (1)
        • rarely caused by Staphylococcus aureus
    • spasmodic croup

  • viral croup (1)
    • is an upper respiratory tract infection (acute laryngotracheobronchitis)
    • affects children 6 months to 12 years of age
    • has a peak incidence at two years of age
    • is the commonnest cause of airway obstruction in children 6 months to 6 years of age (1)
    • boys are affected more often than girls
    • is commonly seen in the fall and winter months
    • parainfluenza viruses (type1, 2, 3) account for the majority of cases
      • most common cause is Human parainfluenza virus 1 (HPIV-1)
      • rarely, other viruses are responsible, for example
        • influenza A and B viruses
        • adenovirus
        • measles
        • RSV (Respiratory syncytial virus)
    • the onset is slower and is usually preceded by a coryzal prodrome (with fever) (1)

  • spasmodic croup (1)
    • associated with the viruses that cause viral croup
    • onset is sudden, without a viral prodrome
    • histology of the subglottic tissues shows noninflammatory oedema
    • tends to recur
    • may represent an allergic reaction to viral antigens
  • often the distinction of the two types is impossible
    • hence sometimes spasmodic croup is considered part of the spectrum of viral croup(1)