To assess the relationship between biomarker concentrations and increased risk of infant bronchiolitis, and early childhood asthma outcomes, we will conduct a nested case-control study. Geometric means of urinary biomarker concentrations for those who develop and do not develop asthma will be calculated separately and compared using the paired t-test. The association between these biomarkers and the risk of asthma and allergic rhinitis will be assessed using odds ratios and their corresponding 95% confidence intervals from adjusted logistic regression models. The potential confounders that will be considered in multivariable analyses will include demographic and exposure characteristics.