Eligible for inclusion were infants younger than 12 months of age with a virologically confirmed clinical diagnosis of RSV LRTD (either a positive direct immunofluorescent assay or ELISA) who were admitted to the nine-bed paediatric intensive care unit (PICU) facility of the VU university medical center for MV during the RSV seasons (autumn and winter) between 2005 and 2007. Infants were excluded if no informed consent was obtained, fraction of inspired oxygen (FiO 2 ) was more than 0.4, corticosteroids were used prior to admission, they were on high-frequency oscillatory ventilation or a haemodynamically significant congenital heart defect (i.e. significant left-to-right shunting with or without pulmonary hypertension) was present.