<prompt> The most common etiological agent for acute bronchiolitis in infancy is ?Influenza virusPara influenza virusRhinovirusRespiratory syncytial virus  <response>: Ans. is d i.e., Respiratory syncytial virus The most common etiological agent for Bronchiolitis is Respiratory synctial virus. RSV is responsible for more than 50 of cases of bronchiolitis. Bronchiolitis o Bronchiolitis is the most common serious acute lower respiratory tract infection in infants and young children. o Most vulnerable group is between the ages of 1 and 6 months. o But the disease can affect children up to 2 years. o More common in males. Organisms causing bronchiolitis o Bronchiolitis is predominantly a viral disease. i RSV most common ii Parainfluenza virus 3, 1, 2 v Mycoplasma pneumoniae iii Adenovirus iv Influenza virus 