The most common etiological agent for acute bronchiolitis in infancy is –

"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 bronchiolitis Bronchiolitis is predominantly a viral disease. i) RSV (mostcommon)  ii) Parainfluenza virus 3, 1, 2        iii) Adenovirus     iv) Influenza virus v) Mycoplasma pneumoniae