Abstract
Many areas of the United States have air pollution levels typically below Environmental Protection Agency (EPA) regulatory limits. Most health effects studies of air pollution use meteorological (e.g., warm/cool) or astronomical (e.g., solstice/equinox) definitions of seasons despite evidence suggesting temporally-misaligned intra-annual periods of relative asthma burden (i.e., “asthma seasons”). We introduce asthma seasons to elucidate whether air pollutants are associated with seasonal differences in asthma emergency department (ED) visits in a low air pollution environment. Within a Bayesian time-stratified case-crossover framework, we quantify seasonal associations between highly resolved estimates of six criteria air pollutants, two weather variables, and asthma ED visits among 66,092 children ages 5–19 living in South Carolina (SC) census tracts from 2005 to 2014. Results show that coarse particulates (particulate matter <10 μm and >2.5 μm: PM10-2.5) and nitrogen oxides (NOx) may contribute to asthma ED visits across years, but are particularly implicated in the highest-burden fall asthma season. Fine particulate matter (<2.5 μm: PM2.5) is only associated in the lowest-burden summer asthma season. Relatively cool and dry conditions in the summer asthma season and increased temperatures in the spring and fall asthma seasons are associated with increased ED visit odds. Few significant associations in the medium-burden winter and medium-high-burden spring asthma seasons suggest other ED visit drivers (e.g., viral infections) for each, respectively. Across rural and urban areas characterized by generally low air pollution levels, there are acute health effects associated with particulate matter, but only in the summer and fall asthma seasons and differing by PM size.
Highlights
In the high-burden fall, we found statistically significant associations with asthma Emergency department (ED) visits that were positive for nitrogen oxides (NOx) (ORIQR: 1.034, 95% CI: 1.009, 1.060), negative for PM2.5 (ORIQR: 0.970, 95% CI: 0.942, 0.998), and positive for particulate matter
We identified increasing asthma disparities across several socio-demographic factors in South Carolina (SC) from 2005–2014, a departure from the plateauing national trend
We uniquely outlined the concept of asthma seasons that were defined by local intra-annual periods of relative burden
Summary
This research was approved (Pro00068172) by the Medical University of South Carolina institutional review board as a part of the SocioEnvironmental Associations with Asthma Increased Risk (SEA-AIR) study. The health outcome data consisted of 66,092 ED visits with a primary diagnosis of asthma (International Classification of Disease 9, ICD9, codes 493.XX) among children ages 5–19 years residing in South Carolina from 2005 to 2014. To the best of our knowledge, the data have population wide coverage, capturing all pediatric ED visits for asthma in SC during the 10-year study period. Diagnostic codes, dates of admittance and discharge, and geographic identifiers were included. Records included geographic identifiers of both ZIP codes and census tracts. ED records were assigned exposure and weather estimates of their billing code census tract, respectively
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