The relationship of respiratory and cardiovascular hospital admissions to the southern California wildfires of 2003
R. J. Delfino, S. Brummel, J. Wu, H. Stern, B. Ostro, M. Lipsett, A. Winer, D. H. Street, L. Zhang, T. Tjoa and D. L. Gillen. 2008. The relationship of respiratory and cardiovascular hospital admissions to the southern California wildfires of 2003. Occup. Environ. Med. 2009;66;189-197.
Note: lead author is Dr. Ralph J. Delfino, Epidemiology Department, School of Medicine, University of California, Irvine, CA
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ABSTRACT
Objective: There is limited information on the public health impact of wildfires. The relationship of cardiorespiratory hospital admissions (n=40 856) to wildfirerelated particulate matter (PM2.5) during catastrophic wildfires in southern California in October 2003 was evaluated.
Methods: Zip code level PM2.5 concentrations were estimated using spatial interpolations from measured PM2.5, light extinction, meteorological conditions, and smoke information from MODIS satellite images at 250 m resolution. Generalised estimating equations for Poisson data were used to assess the relationship between daily admissions and PM2.5, adjusted for weather, fungal spores (associated with asthma), weekend, zip code-level population and sociodemographics.
Results: Associations of 2-day average PM2.5 with respiratory admissions were stronger during than before or after the fires. Average increases of 70 mg/m3 PM2.5 during heavy smoke conditions compared with PM2.5 in the pre-wildfire period were associated with 34% increases in asthma admissions. The strongest wildfire-related PM2.5 associations were for people ages 65–99 years (10.1% increase per 10 mg/m3 PM2.5, 95% CI 3.0% to 17.8%) and ages 0–4 years (8.3%, 95% CI 2.2% to 14.9%) followed by ages 20–64 years (4.1%, 95% CI 20.5% to 9.0%). There were no PM2.5–asthma associations in children ages 5–18 years, although their admission rates significantly increased after the fires. Per 10 mg/m3 wildfire-related PM2.5, acute bronchitis admissions across all ages increased by 9.6% (95% CI 1.8% to 17.9%), chronic obstructive pulmonary disease admissions for ages 20–64 years by 6.9% (95% CI 0.9% to 13.1%), and pneumonia admissions for ages 5–18 years by 6.4% (95% CI 21.0% to 14.2%). Acute bronchitis and pneumonia admissions also increased after the fires. There was limited evidence of a small impact of wildfire-related PM2.5 on cardiovascular admissions.
Conclusions: Wildfire-related PM2.5 led to increased respiratory hospital admissions, especially asthma, suggesting that better preventive measures are required to reduce morbidity among vulnerable populations.
We present here the largest study to date evaluating the relationships of hospital admissions for cardiorespiratory outcomes to wildfire-associated PM2.5 using data from the catastrophic wildfires that struck southern California in the autumn of 2003. We linked PM2.5 concentrations estimated at the zip code level to a population-based dataset of hospital admissions using spatial time series analyses of data before, during and after the fires. Strong, dry winds from inland deserts fanned flames from nine distinct fires, which burned nearly three quarters of a million acres and destroyed approximately 5000 residences and outbuildings. The wildfires generated large amounts of dense smoke that covered much of urban southern California (2003 population of 20.5 million). PM2.5 and PM10 concentrations far exceeded US federal regulatory standards. The goal of the present study is to assess the impact of this large wildfire event on serious morbidity.
