Croup is usually caused by a viral infection with parainfluenza virus, respiratory syncytial virus (RSV), or influenza viruses A and B. These viruses are commonly present in the air, especially during the late fall and winter. One bacterium that can cause croup is Hemophilus influenzae.

Croup occurs most often in children between 6 months and 3 years of age.

The characteristic barking cough and noisy breathing (stridor) is caused by swelling in the upper airway (larynx, trachea, and bronchi). The child's breathing becomes more difficult and requires increasing physical effort. The child may be physically tired but is unable to rest because of the increased breathing effort.

The child may be restless, have a fever, and be working hard to keep breathing. Extra effort to breathe may be noticed as wider opening of the nostrils during inhalation (nasal flaring); increased use of the muscles in the neck and chest; and unwillingness to lie down, rest, eat, or drink. In severe cases the child's lips and fingers may turn blue (cyanosis), indicating inadequate oxygen supply.

In severe cases of croup, there may also be a bacterial super-infection of the upper airway. This condition is called bacterial tracheitis and requires hospitalization and intravenous antibiotics. If the epiglottis becomes infected, the entire windpipe can swell shut, a potentially fatal condition called epiglottitis.

• Breathing difficulty
• Barking, spasmodic cough
• High-pitched sound when breathing in (stridor)
• Rapid breathing
• Skin discoloration, bluish caused by lack of oxygen
• Increased use of neck and chest muscles (intercostal retractions)

A physical examination shows chest retractions with breathing. Listening to the chest through a stethoscope (auscultation) reveals prolonged inspiration or expiration, wheezing, and decreased breath sounds.

An examination of throat may reveal a red epiglottis. A neck X-ray may reveal a foreign object or narrowing of the trachea.

Mild illness may be treated at home with supportive measures. Parents should stay calm to help the child to stay calm.

Warm or cool humidified air should be provided. A hot shower can provide warm steam, hold the child in the bathroom for 20 minutes so he or she can breath the hunidified air. (Do not place the child in the shower.) Taking the child outside into cold air may be helpful as well.

Serious illness requires hospitalization. Increasing or persistent breathing difficulty, fatigue, bluish coloration of the skin, or dehydration indicates the need for medical attention or hospitalization.

Aerosolized racemic epinephrine as well as oral dexamethasone (a steroid) are used to help to shrink the upper airway swelling. Oxygen and humidity may be provided in an oxygen tent placed over a crib. A bacterial infection requires antibiotic therapy.

Increasing obstruction of the airway requires intubation (placing a tube through the nose or mouth through the larynx into the main air passage to the lungs). Intravenous fluids are given for dehydration. In some cases, corticosteroids are prescribed.

Viral croup usually goes away in 3 to 7 days. The outcome for bacterial croup is good with prompt treatment.

If an airway obstruction is not treated promptly, respiratory distress (severe difficulty breathing) and respiratory arrest can occur.

• Respiratory distress
• Respiratory arrest
• Epiglottitis
• Bacterial tracheitis
• Atelectasis (collapse of part of the lung)
• Dehydration

In most cases, you should apply home treatment first. Call your health care provider if severe symptoms persist for more than 1 hour.

Call 911 (or your local emergency number) or go to the emergency room if you see any of the following:

• Severe breathing difficulty
• Bluish coloration of the skin
• Fatigue
• Dehydration
• Unconsciousness

If your child is extremely irritable and has excessive drooling, he or she could have epiglottitis. Call 911 (or your local emergency number) or go to the emergency room for immediate assistance.