Definition of Bronchiolitis:

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

Causes, incidence, and risk factors:

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)