The relationship of high PM^sub 2.5^ days and subsequent asthma-related hospital encounters during the fireplace season in Phoenix, AZ, 2008-2012

Exposure to particulate matter less than 2.5 [mu]m in diameter (PM2.5) exacerbates asthma and increases mortality. In Phoenix, AZ, the highest PM2.5 values frequently occur during the winter fireplace season and air quality health standards are often exceeded during the Christmas and New Year's holidays. It was clear that enhanced messaging was needed by air quality and public health authorities to discourage biomass fires (BMF) on days when unhealthful levels of pollution were likely to be caused by that activity. Demonstrating adverse health outcomes would bolster this effort. We conducted this study to evaluate associations between elevated PM2.5 exposures during the fireplace season and asthma-related hospital admissions in Phoenix; days with average PM2.5 > 35 [mu]g/m3 were categorized as elevated PM2.5 exposure. We used hospital discharge data to identify patients with an asthma-related hospital encounter and who lived within an 8-km radius of a PM2.5 monitor. To estimate the risk of a hospital encounter following an elevated PM2.5 event, we used generalized estimating equations, specified with a Poisson distribution, and exposure lags of 0-3 days. Controlling for influenza, temperature, humidity, rain, and year, these analyses generated elevated estimates of emergency department visit risk among adults on lag days 2 (relative risk [RR] 1.19; 95 % CI 1.06, 1.34) and 3 (RR 1.20, 95 % CI 1.05, 1.37). Elevated PM2.5 was not associated with hospital encounters among children. Our findings suggest that adults may be at elevated risk of asthma-related hospital encounters during the fireplace season.