Croup, also known as laryngotracheobronchitis, is a type of respiratory infection that is usually caused by a virus. The infection leads to swelling inside the trachea, which interferes with normal breathing and produces the classic symptoms of "barking" cough, stridor, and a hoarse voice. Fever and runny nose may also be present. These symptoms may be mild, moderate, or severe. Often it starts or is worse at night. It normally lasts one to two days.


Croup affects about 15% of children, and usually presents between the ages of 6 months and 5–6 years. It accounts for about 5% of hospital admissions in this population. In rare cases, it may occur in children as young as 3 months and as old as 15 years.


Croup can be caused by a number of viruses including parainfluenza and influenza virus. Rarely is it due to a bacterial infection. 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. Further investigations—such as blood tests, X-rays, and cultures—are usually not needed.

Signs and symptoms

Croup is characterized by a "barking" cough (commonly referred to as a "seal-bark cough"), stridor, hoarseness, and difficulty breathing which usually worsens at night. The stridor is worsened by agitation or crying, and if it can be heard at rest, it may indicate critical narrowing of the airways. As croup worsens, stridor may decrease considerably.

Other symptoms include fever, coryza (symptoms typical of the common cold), retractions. Drooling or a very sick appearance may indicate other medical conditions, such as epiglottitis.


The viral infection that causes croup leads to swelling of the larynx, trachea, and large bronchi due to infiltration of white blood cells (especially histiocytes, lymphocytes, plasma cells, and neutrophils). Swelling produces airway obstruction which, when significant, leads to dramatically increased work of breathing and the characteristic turbulent, noisy airflow known as stridor.

Croup is typically diagnosed based on signs and symptoms. The first step is to exclude other obstructive conditions of the upper airway, especially epiglottitis, foreign body airway obstructions and/or angioedema.


Children with croup typically need to be kept as calm as possible. Steroids are given routinely, with nebulised adrenaline used in severe cases. Children with clinical indicators of hypoxaemia should be administered oxygen and those with severe croup may be hospitalized for observation. If oxygen is needed, "blow-by" administration (holding an oxygen source near the child's face) is recommended, as it causes less agitation than use of a mask.


Corticosteroids such as prednisolone, dexamethasone and budesonide have been shown to improve outcomes in children with all severities of croup. Significant relief is obtained as early as two hours after administration.


Moderate to severe croup may be improved temporarily with nebulised adrenaline. While adrenaline typically produces a reduction in croup severity within 10–30 minutes, the benefits last for only about 2 hours and the patient may benefit from concurrent treatment with oral steroids. If the condition remains improved for 2–4 hours after treatment and no other complications arise, the child is typically discharged from the hospital.

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