A 24 Month Observational Study of Infants 3-24 Months, Who Suffer an Acute Episode of Respiratory Infection and Wheezing Illness

Inclusion Criteria: * Documented informed consent from legal guardian prior to study procedures * Age: 3-24 months at the time of visit 1 * Severe lower respiratory wheezing illness confirmed by auscultation requiring hospitalization or acute care (Emergency Department care or unscheduled ambulatory care) Exclusion Criteria: * No prior hospital admissions for wheezing illnesses * No prior diagnosis of asthma or Reactive Airways Disease * More than 1 prior episode of wheezing confirmed by auscultation * No congenital or chronic disease which would negatively affect the conduct of the study (e.g. childhood cancer, cystic fibrosis, interstitial lung disease, prior aero-digestive surgery) * No diagnosis of bronchopulmonary dysplasia * No premature birth (gestational age \< 32 weeks) * Daily treatment with a daily asthma controller (e.g. Montelukast, inhaled corticosteroid)