Croup (/kruːp/ KROOP), also known as croupy cough, 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/brassy" cough, inspiratory stridor, and a hoarse voice. Fever and runny nose may also be present. These symptoms may be mild, moderate, or severe. It often starts or is worse at night and normally lasts one to two days.
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.