Objective: There is limited information on the public health impact of wildfires, expected to grow given the influence of global warming. We evaluated the relationship of cardiorespiratory hospital admissions (N=40,856) to wildfire-related particulate matter (PM2.5) during catastrophic wildfires that struck southern California in October 2003.
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 250m resolution. We used generalized estimating equations for Poisson data 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 two-day average PM2.5with respiratory admissions were stronger during as compared with before or after the fire. Average increases of 70 μg/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 μg/m3 PM2.5, 95% CI: 3.0, 17.8%) and ages 0-4 years (8.3%, 95% CI: 2.2, 14.9%) followed by ages 20-64 years (4.1%, 95% CI: -0.5, 9.0%). There were no PM2.5-asthma associations in children ages 5-18 years, although their admission rates significantly increased after the fire. Per 10 μg/m3 wildfire-related PM2.5, acute bronchitis admissions across all ages increased by 9.6% (95% CI: 1.8, 17.9), COPD admissions for ages 20-64 years increased by 6.9% (95% CI: 0.9, 13.1), and pneumonia admissions for ages 5-18 years increased by 6.4% (95% CI: -1.0, 14.2). Acute bronchitis and pneumonia admissions also increased after the fire. 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.
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