<2yr old (peak 2-6mo age)
Respiratory syncytial virus (RSV) causes ~70% of cases
Preemies, neonates, congenital heart disease are at risk for serious disease
Peaks in winter
Duration = 7-14d (worst during days 3-5)
Inflammation, edema, and epithelial necrosis of bronchioles
Bronchiolitis 
Airway obstruction
Croup
Anaphylaxis
Mediastinitis
Angioedema
Bacterial tracheitis
Aspirated foreign body