The term croup is used in an inclusive way to identify several different respiratory illnesses of children manifested by varying degrees of inspiratory stridor, cough, and hoarseness due to upper-airway obstruction. Classically croup was a manifestation of diphtheria. In the twentieth century, many other infectious causes of croup syndromes are recognized, and in addition, similar illnesses can be caused by noninfectious processes.

A classification of crouplike illnesses is presented in Table VIII.30.1. Although long-term obstruction in the glottic and subglottic regions can lead to chronic illnesses, croup syndromes are described here as acute self-limited or fatal illnesses. Most cases of croup today are either laryngotracheitis or spasmodic croup.

Etiology

Acute epiglottitis (inflammation of the epiglottis) is virtually always caused by Haemophilus influenzae type B; rare cases have been due to Streptococcus pneumoniae and Staphylococcus aureus. Laryngitis is usually due to the common respiratory viral agents, the most important of which are adenoviruses and influenza viruses.

Laryngotracheitis and spasmodic croup are common illnesses in children and are due to viruses or Mycoplasma pneumoniae. The most important agent is parainfluenza virus type 1. This virus, as well as parainfluenza type 2 and influenza A and B viruses, results in outbreaks of disease. In areas of the world where diphtheria toxoid immunization is not carried out, laryngotracheitis is also caused by Corynebacterium diphtheria.

Laryngotracheobronchitis and laryngotracheobronchiopneumonitis are frequently caused by the same viruses that cause laryngotracheitis. These two illnesses are caused also by S. aureus, Streptococcus pyogenes, S. pneumoniae, and H. influenzae.