Bronchiolitis is the leading cause of hospitalizations among infants in the U.S. Two major respiratory viruses—respiratory syncytial virus (RSV) and rhinovirus (RV)—account for 85% of severe bronchiolitis (bronchiolitis resulting in hospitalization). While bronchiolitis has been considered a single disease entity and currently available management does not vary by causative virus,emerging evidence suggests heterogeneity in the clinical manifestations and pathobiology of bronchiolitis by virus. For example, epidemiological research has shown that causative viruses are associated with distinct risks of both acute (e.g., illness severity) and chronic (e.g., incident asthma) outcomes in childhood