Croup is most often caused by viruses, such as parainfluenza RSV, measles, adenovirus, and influenza. It tends to appear in children between 3 months and 5 years old, but it can happen at any age. Some children are more likely to get croup and may get it several times. It is most common between October and March, but can occur at any time of the year.
More severe cases of croup may be caused by bacteria. This condition is called bacterial tracheitis.
Croup may also be caused by:
Breathing in something that irritates your airway
The main symptom of croup is a cough that sounds like a seal barking.
Most children will have mild cold symptoms for several days before the barking cough becomes evident. As the cough gets more frequent, the child may have trouble breathing or stridor (a harsh, crowing noise made when breathing in).
Croup is typically much worse at night. It often lasts 5 or 6 nights. The first night or two are most often the worst. Rarely, croup can last for weeks. Talk to your child's doctor if croup lasts longer than a week or comes back often.
Exams and Tests
Children with croup are most often diagnosed based on the parent's description of the symptoms and a physical exam. Sometimes a doctor will listen to a child cough over the phone to identify croup. In a few cases, x-rays or other tests may be needed.
A physical exam may show chest retractions with breathing. When listening to the child's chest through a stethoscope, the health care provider may hear:
Hall CB, McBride JT. Acute laryngotracheobronchitis (croup). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2009:chap 56.
Roosevelt GE. Acute inflammatory upper airway obstruction (croup, epiglottitis, laryngitis, and bacterial tracheitis). In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 377.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.