Causes of premature bronchiolitis

Respiratory syncytial virus (RSV) is the main causative agent of bronchiolitis (75% of cases), especially during epidemics among hospitalised patients. The second most common cause is the rhinovirus (cold virus).  

Other viruses that also cause bronchiolitis, although less frequently, include parainfluenza, metapneumovirus, influenza, adenovirus, coronavirus and human bocavirus.  

Viral co-infection occurs in one third of infants hospitalised with bronchiolitis. In other words, they are infected by more than one virus at the same time.

Furthermore, lower respiratory tract infections and episodes of wheezing (a whistling sound when breathing) in infants may be associated with mycoplasma pneumoniae infection, the bacteria that causes pneumonia.