Modification of the Effect of Ambient Air Pollution on Pediatric Asthma Emergency Visits: Susceptible Subpopulations

Abstract

Epidemiologic and experimental research supports the conclusion that certain outdoor air pollutants cause exacerbations of asthmatic symptoms among children with asthma.1,2 Similarly, there is a growing body of literature describing how in utero and early life experiences affect physiological development and influence sensitivity to environmental factors throughout life.3 Unfortunately, most large population-based studies of associations between short-term changes in ambient air pollutant concentrations and asthma exacerbations have lacked data on early-life risk factors, whereas the cohort studies that include such information are often too small to support investigation of effect-measure modification among potentially susceptible subgroups. In the U.S. state of Georgia, data on live birth records have been linked with pediatric emergency department visits by staff at the Office of Health Indicators for Planning at the Georgia Department of Public Health. Additionally, in metropolitan Atlanta there are several long-running air quality measurement campaigns that include, among other more commonly measured pollutants, daily measurements from four monitoring stations of speciated particulate matter less than 2.5 microns in diameter (PM2.5). We used these two data resources to estimate the rate ratio (RR) relating short-term changes in air pollutant concentrations to emergency department (ED) visits for asthma or wheeze and to investigate whether there was evidence for effect-measure modification of the RR by various risk factors available from the linked dataset. Although we examined effect-measure modification for eight different factors, we had particular a priori interest in investigating whether susceptibility might have varied by gestational age, as accumulating evidence suggests that children born preterm have long-term decrements in lung function.4,5