Large-scale agricultural burning and asthma emergency department visits in the U.S. state of Kansas

Abstract

Background: Prescribed agricultural burning is a common land management practice, but little is known about the respiratory health effects from the resulting smoke exposure. We examined the association between smoke from prescribed burning and asthma in the U.S. state of Kansas. Methods: We analyzed a zip code-level daily time series of primary asthma emergency department (ED) visits and environmental variables for years 2009 - 2011 (n=62,105); analyses were restricted to the months when prescribed burning is common in Kansas (February - May). Given limited monitoring data, we formulated a measure of smoke exposure using non-traditional datasets, including fire radiative power and locational attributes from remote sensing data sources and surface wind characteristics from model-based earth observations. We then assigned a population-weighted potential smoke impact factor (PSIF) to each zip code, based on fire intensity, smoke transport and proximity (to fire) considerations. We used Poisson generalized linear models to estimate the association between PSIF (both as binary and 4-level categorical variables) and asthma ED visits. Results: During the study period, prescribed burning was used to clear approximately 8 million acres in Kansas. Same-day PSIF was associated with a 3% increase in the rate of asthma ED visits when adjusting for month, year, zip code, meteorology, day of week, holidays, and correlation within zip codes (rate ratio [RR]:1.03; 95% confidence interval [CI]:0.97, 1.09). When comparing tertiles of same-day exposure to a reference group of no exposure, adjusted rates of asthma ED visits were elevated for the two lowest tertiles, but did not increase monotonically (RR[CI] from lowest to highest exposure: 1.06[0.95, 1.18], 1.05[0.97, 1.14], 1.00[0.93, 1.08]). Conclusions: Our preliminary results are suggestive of an association between smoke from prescribed burning and asthma ED visits. Elucidating these associations will help guide public health programs that address population-level exposure to smoke from prescribed burning.