Association of trees and other vegetation near homes with asthma exacerbation in children

Abstract

Background. Vegetated landscapes (i.e., greenspace) may increase or decrease risk of asthma exacerbation through effects on pollen levels, localized climates (e.g., heat islands), air pollution, or child’s behaviors.Methods. We investigated the association between neighborhood greenspace and pediatric asthma exacerbation (age <18 years) in the City of Philadelphia, by conducting a case-control study based on electronic health records (EHR) from the Children’s Hospital of Philadelphia (CHOP) Care Network. Our study included cases from 8017 outpatient clinic visits, 5953 emergency department (ED) visits, and 4401 inpatient encounters, with controls selected from non-exacerbation clinical encounters for asthma. We studied various greenspace measures, including overall greenness (i.e., vegetation density), tree canopy, grass/shrub coverage, and impervious landcover, within various buffer sizes surrounding the child’s residence. We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI), adjusting for child- and neighborhood level sociodemographic factors.Results. Lower odds of asthma exacerbation were observed in association with high levels of greenspace near the home (>75th percentile vs. ≤25th percentile) for ED cases, such as reduced odds of ED visits by 29% with high tree canopy coverage (OR=0.71, 95% CI= 0.61, 0.83), and 16% with high grass/shrub coverage (OR=0.84, 95% CI: 0.74, 0.97). Impervious surface landcover near the home was associated with greater odds of asthma exacerbation for ED (high vs. low: OR=1.50, 95% CI: 1.28, 1.75) and inpatient cases (OR=1.20, 95% CI: 1.02, 1.42). Small reductions in risk of outpatient clinic cases or inpatient cases in association with greater amounts of vegetation near the home were not statistically significant in the best-fitting models.Conclusions. Our findings suggest a protective effect of residential neighborhood greenspace against asthma exacerbation; however, differing results among treatment settings requires further assessment of confounding by indication and effect modification.