Which of the following is the MOST common organism causing bronchiolitis?

RSV is the most common viral cause of acute viral bronchiolitis. Less common causes of acute bronchiolitis are parainfluenza, human metapneumovirus, influenza, adenovirus, Mycoplasma, Chlamydia, Ureaplasma, Bocavirus, and Pneumocystis. Acute bronchiolitis is diagnosed in children less than 2 years of age. Diagnosis is made upon the clinical findings of an upper respiratory infection that has progressed to cough, tachypnea, respiratory distress, and crackles or wheeze by physical examination. The most common complication of bronchiolitis is super infection with Streptococcus pneumoniae leading to pneumonia. Ref: Federico M.J., Stillwell P., Deterding R.R., Baker C.D., Balasubramaniam V., Zemanick E.T., Sagel S.D., Halbower A., Burg C.J., Kerby G.S. (2012). Chapter 19.