Bronchiolitis is swelling and mucus buildup in the smallest air passages in the lungs (bronchioles), usually due to a viral infection.

Bronchiolitis usually affects children under the age of 2, with a peak age of 3 - 6 months. It is a common, and sometimes severe illness. Respiratory syncytial virus (RSV) is the most 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 fluids, or by airborne droplets. Although RSV generally causes only mild symptoms in an adult, it can cause 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 their first year, more than half of all infants have been exposed to RSV.

Risk factors include:

• Exposure to cigarette smoke
• Age younger than 6 months old
• Living in crowded conditions
• Lack of breast-feeding
• Prematurity (being born before 37 weeks gestation)

Images

Normal lungs and alveoli

Bronchiolitis

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Bronchiolitis Symptoms

Review Date: 11/02/2009
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)