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Bronchiolitis Symptoms and Causes

Bronchiolitis is swelling and mucus buildup in the smallest air passes 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 to 6 months. It is a common, and sometimes severe illness. Respiratory syncytial virus (RSV) is the most common cause.