Early-life exposure to residential greenness and risk of asthma in a U.S. bronchiolitis cohort

Introduction: Severe bronchiolitis (i.e., bronchiolitis requiring hospitalization) is linked to childhood asthma development. Despite a growing understanding of risk factors for developing post-bronchiolitis asthma, protective factors remain unclear. In this study, we aimed to investigate whether exposure to residential greenness between birth and bronchiolitis hospitalization is associated with asthma and atopic asthma development by age 6 years.

Methods: We analyzed a US severe bronchiolitis cohort from hospitalization to age 6 years, investigating how the normalized difference vegetation index (NDVI) and chlorophyll index green (CI green), measured in small (100 m) and large (500 m) radiuses around homes, relate to asthma and atopic asthma by age 6 years. We also explored whether maternal antibiotic use, daycare attendance, and respiratory virus type during hospitalization act as effect modifiers.

Results: The study cohort included 861 infants, with 239 (28%) developing asthma by age 6 years-152 atopic, 17 nonatopic, and 70 unclassified. Early life residential exposure to high NDVI and CI green levels was associated with lower odds of asthma (OR_Adj for NDVI within a 100 m radius, 0.18; 95% CI, 0.05-0.78; and OR_Adj for CI green levels within a 100 m radius, 0.53; 95% CI, 0.31-0.90). Associations also were significant for the development of atopic asthma (OR_Adj 0.16; 95% CI, 0.03-0.96; and OR_Adj 0.46; 95% CI, 0.25-0.92; respectively). Results were similar for the 500 m radius exposures. No effect modification was noted.

Conclusion: In a U.S. bronchiolitis cohort, exposure to residential greenness between birth and bronchiolitis hospitalization is linked to lower asthma and atopic asthma risk by age 6 years.