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 is a viral infection of the voice box (larynx) and windpipe ( trachea ) associated with signs of a respiratory infection, such as a runny nose or cough . It's also a very common ailment of childhood.
The cough and other symptoms of croup are the result of swelling around the vocal cords (larynx), windpipe (trachea) and bronchial tubes (bronchi). When a cough forces air through this narrowed passage, the swollen vocal cords produce a noise similar to a seal barking. Likewise, taking a breath often produces a high-pitched whistling sound (stridor).
Croup is a condition that swells and irritates the upper airways. The same viruses that cause the common cold also cause croup, and most cases happen in the fall and early winter.
Dr. Mersch received his Bachelor of Arts degree from the University of California, San Diego, and prior to entering the University Of Southern California School Of Medicine, was a graduate student (attaining PhD candidate status) in Experimental Pathology at USC. He attended internship and residency at Children's Hospital Los Angeles.
Croup is caused by an acute viral infection of the upper respiratory tract. It is also called laryngotracheobronchitis since it affects the larynx, trachea, and bronchi . This infection results in inflammation, increased mucus production, and swelling of the upper airways. Although croup usually resolves on its own, some children with croup will require admission to the hospital. Croup continues to be one of the most common causes of respiratory distress in young children.
Croup is a common respiratory problem in young children. It tends to occur in the fall and winter. Its main symptom is a harsh, barking cough . Croup causes swelling and narrowing in the voice box, windpipe, and breathing tubes that lead to the lungs . This can make it hard for your child to breathe.