Lots of things. Could be rsv, hmpv, adenovirus, flu, paraflu, rhinovirus etc. Watch http://www. Youtube. Com/watch? V=5teb03heixw&feature=related to learn more.
Virus- could be RSV. Viral colds are the most common cause of bronchilitis in babies. Many viruses can be the culprit. Rsv (respiratory syncitial virus) is a very common cause, especially in premature infants. Children under two years of age are most at risk and the younger the child, potentially the more severe the symptoms could be.
Virus (usually RSV) Bronchiolitis is caused by a viral infection, usually RSV (respiratory syncytial virus.) it adults and older kids, it usually just causes a "common cold." in infants, though, it can also cause wheezing and breathing problems which can sometimes be severe.