Bronchiolitis is the leading cause of hospitalization of infants and young 
children worldwide. Respiratory syncytial virus (RSV) is the most common cause 
of bronchiolitis in infants. Studies conducted using molecular diagnostic assays 
confirmed that RSV accounts for over 50% of bronchiolitis in young children 
requiring hospitalization. Those studies demonstrate that it is common to 
identify RSV in association with a second viral agent but it is yet unclear 
whether the simultaneous detection of two or even three viruses is associated 
with increased disease severity. Despite extensive efforts, a vaccine for 
prevention of RSV infection is not yet available. Palivizumab a humanized 
monoclonal antibody directed against the F protein of RSV is the only agent 
licensed to prevent severe RSV disease in high-risk children. Among the new 
antivirals being developed for treatment of RSV infections, an RNA-interference 
based agent has demonstrated promising results for treatment of lung transplant 
recipients with acute RSV infection.