ABSTRACT
By far the most frequent cause of severe episodes of wheezing during infancy and early childhood is infection with the respiratory syncytial virus (RSV). In the USA alone approximately 100,000 hospitalizations from lower respiratory illnesses (LRI) due to RSV (RSV-LRI) occur each year1 and approximately 500 deaths/year are attributed to these infections.2 Although virtually all children have evidence of having had an RSV infection by the end of the second year of life,3 only a fraction develop clinical manifestations of RSV-LRI.
