Croup (/kruːp/ KROOP), also known as croupy cough, is a type of respiratory infection that is usually caused by a virus.

[2] The infection leads to swelling inside the trachea, which interferes with normal breathing and produces the classic symptoms of "barking/brassy" cough, inspiratory stridor and a hoarse voice.

[5] Croup is typically diagnosed based on signs and symptoms after potentially more severe causes, such as epiglottitis or an airway foreign body, have been ruled out.

[11] Croup is characterized by a "barking" cough, stridor, hoarseness, and difficult breathing which usually worsens at night.

[5] The stridor is worsened by agitation or crying, and if it can be heard at rest, it may indicate critical narrowing of the airways.

[5] Viral croup or acute laryngotracheitis is most commonly caused by parainfluenza virus (a member of the paramyxovirus family), primarily types 1 and 2, in 75% of cases.

[3] Other viral causes include influenza A and B, measles, adenovirus and respiratory syncytial virus (RSV).

[5] Spasmodic croup is caused by the same group of viruses as acute laryngotracheitis, but lacks the usual signs of infection (such as fever, sore throat, and increased white blood cell count).

[5] Swelling produces airway obstruction which, when significant, leads to dramatically increased work of breathing and the characteristic turbulent, noisy airflow known as stridor.

[12] Other investigations (such as blood tests and viral culture) are discouraged, as they may cause unnecessary agitation and thus worsen the stress on the compromised airway.

[4] While viral cultures, obtained via nasopharyngeal aspiration, can be used to confirm the exact cause, these are usually restricted to research settings.

[5] It is the sum of points assigned for five factors: level of consciousness, cyanosis, stridor, air entry, and retractions.

[5] At one time, croup referred to a diphtherial disease, but with vaccination, diphtheria is now rare in the developed world.

[12] In very rare severe cases of croup that result in respiratory failure, emergency intubation and ventilation may be required.

[13] Corticosteroids, such as dexamethasone and budesonide, have been shown to improve outcomes in children with all severities of croup, however, the benefits may be delayed.

[4] While epinephrine typically produces a reduction in croup severity within 10–30 minutes, the benefits are short-lived and last for only about 2 hours.

[2][4] If the condition remains improved for 2–4 hours after treatment and no other complications arise, the child is typically discharged from the hospital.

The noun describing the disease originated in southeastern Scotland and became widespread after Edinburgh physician Francis Home published the 1765 treatise An Inquiry into the Nature, Cause, and Cure of the Croup.

His death in 1807 left Napoleon without an heir and contributed to his decision to divorce from his wife, the Empress Josephine de Beauharnais.

[26] Preston Brooks, a pro-slavery, pre-Civil War US congressman from South Carolina died unexpectedly from a violent attack of croup on January 27, 1857, a few weeks before the March 4 start of the new congressional term to which he had been re-elected.