The TCRI is a large and comprehensive prospective epidemiologic study of mothers and their biologic children enrolled during infancy with a clinically significant LRTI or URI who are being followed through early childhood. This study will provide important information about the role of infant respiratory viral infection severity, aetiology, biomarkers and predictors important in the development of early childhood asthma and allergic rhinitis. The TCRI is additionally unique because it is designed in parallel with a large retrospective birth cohort of over 95 000 mother-infant dyads with similar objectives to investigate the role of respiratory viral infection severity and aetiology in the development of asthma.