Bronchiolitis is an inflammation of the small passages in the lungs (bronchioles), usually caused by a viral infection.

Bronchiolitis usually affects children under the age of 2, with a peak age of 3 to 6 months. It is a common, sometimes severe illness. Respiratory syncytial virus (RSV) is one common cause. Other viruses that can cause bronchiolitis include:

• Adenovirus
• Influenza
• Parainfluenza

The virus is transmitted from person to person by direct contact with nasal secretions or by airborne droplets. Although RSV generally causes only mild symptoms in an adult, it can cause a severe illness in an infant.

Bronchiolitis is seasonal and appears more often in the fall and winter months. It is a very common reason for infants to be hospitalized during winter and early spring. It is estimated that by the first year, more than half of all infants have been exposed to RSV.

Risk factors include:

• Being exposed to cigarette smoke
• Being younger than 6 months old
• Living in crowded conditions
• Never being breastfed
• Prematurity (born before 37 weeks gestation)

Some children have infections with few or minor symptoms.

Bronchiolitis begins as a mild upper respiratory infection that, over a period of 2 to 3 days, can develop into increasing respiratory distress with wheezing and a "tight" wheezy cough.

The infant's breathing rate may increase a lot (tachypnea), and the infant may become irritable or anxious-looking. If the disease is severe enough, the infant may turn bluish (cyanotic), which is an emergency.

As the effort of breathing increases, parents may see the child's nostrils flaring with each breath and the muscles between the ribs retracting (intercostal retractions) as the child tries to breathe in air. This can be exhausting for the child, and very young infants may become so tired that they have difficulty maintaining breathing.

Symptoms include:

• Bluish skin due to lack of oxygen (cyanosis)
• Cough, wheezing, shortness of breath, or difficulty breathing
• Fever
• Intercostal retractions
• Nasal flaring in infants
• Rapid breathing (tachypnea)

Signs include:

• Decreased blood oxygen
• Wheezing and crackling sounds heard through stethoscope exam of chest

Tests include:

• Blood gases
• Chest x-ray
• Nasal fluid cultures (to determine which virus is present)

Sometimes, no treatment is necessary.

Supportive therapy can include:

• Chest clapping
• Clear fluids
• Humidified air
• Oxygen
• Rest

Antibiotics are not effective against viral infections. Medicines used in the hospital can include albuterol (a medication normally used in asthma) or steroids.

In extremely ill children, antiviral medications (such as ribavirin) are sometimes used. Antiviral treatment may decrease the severity and duration of the illness. To be effective, these medications must be given early in the course of the illness.

Usually, the symptoms get better within a week, and breathing difficulty usually improves by the third day. The mortality rate is less than 1%.

• Airways disease, including asthma, later in life
• Respiratory failure
• Secondary infection, such as pneumonia

Call your health care provider immediately, or go to the emergency room if the child with bronchiolitis:

• Becomes lethargic
• Develops a bluish color in the skin, nails, or lips
• Develops rapid, shallow breathing
• Has a cold that suddenly worsens
• Has difficulty breathing
• Flares nostrils or retracts chest muscles in an effort to breathe

Most cases of bronchiolitis are not easily preventable because the viruses that cause the disorder are common in the environment. Careful attention to hand washing, especially around infants, can help prevent the spread of respiratory viruses.

Family members with an upper respiratory infection should be especially careful around infants. Wash your hands often, especially before handling the child.

At this date, there is no RSV vaccine available. However, there is an effective product, called palivizumab (Synagis), for infants who are at high risk of developing severe disease from RSV. Ask your child's doctor whether this medication is right for your child.