For the prospective part of the study, all infants up to 1 year of age presenting to the ED for bronchiolitis from November 1st, 2011 to March 30th, 2012 will be included in this observational study. For the retrospective part of the study, data of all infants up to 1 year of age who were seen in the ED for bronchiolitis from November 1st, 2009 and March 30th, 2010 and from November 1st, 2010 and March 30th, 2011 will be analyzed.