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 wind pipe, 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.