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