Bronchiolitis By Rajeev Bhatia, MD, Phoenix Children's Hospital Reviewed / Revised Jan 2022 | Modified Sep 2022 View Patient Education Etiology Pathophysiology Symptoms and Signs Diagnosis Prognosis Treatment Key Points Topic Resources Wheezing Crackles Bronchiolitis is an acute viral infection of the lower respiratory tract affecting infants < 24 months and is characterized by respiratory distress, wheezing, and / or crackles.