The relationship of respiratory and cardiovascular hospital admissions to the southern California wildfires of 2003

Ralph J Delfino ^1*, Sean Brummel ², Jun Wu ¹, Hal Stern ², Bart Ostro ³, Michael Lipsett ⁴, Arthur Winer ⁵, Donald H Street ⁶, Lixia Zhang ⁴, Thomas Tjoa ¹ and Daniel L Gillen ²

¹ Department of Epidemiology, School of Medicine, University of California, Irvine, United States
² Dept of Statistics, School of Information and Computer Science, University of California, Irvine, United States
³ Air Pollution Epidemiology Section, California Office of Environmental Health Hazard Assessment, United States
⁴ Exposure Assessment Section, Environmental Health Investigations Branch, CA Dept of Health Services, United States
⁵ Department of Environmental Health Sciences, School of Public Health, University of CA, Los Angeles, United States
⁶ Independent consultant, Salem, OR, United States

^* To whom correspondence should be addressed. E-mail: rdelfino{at}uci.edu.

Accepted 18 August 2008

Abstract

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 (PM_2.5) during catastrophic wildfires that struck southern California in October 2003.

Methods: Zip-code level PM_2.5 concentrations were estimated using spatial interpolations from measured PM_2.5, 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 PM_2.5, adjusted for weather, fungal spores (associated with asthma), weekend, zip code-level population and sociodemographics.

Results: Associations of two-day average PM_2.5with respiratory admissions were stronger during as compared with before or after the fire. Average increases of 70 µg/m³ PM_2.5 during heavy smoke conditions compared with PM_2.5 in the pre-wildfire period were associated with 34% increases in asthma admissions. The strongest wildfire-related PM_2.5 associations were for people ages 65-99 years (10.1% increase per 10 µg/m³ PM_2.5, 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 PM_2.5-asthma associations in children ages 5-18 years, although their admission rates significantly increased after the fire. Per 10 µg/m³ wildfire-related PM_2.5, 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 PM_2.5 on cardiovascular admissions.

Conclusions: Wildfire-related PM_2.5 led to increased respiratory hospital admissions, especially asthma, suggesting that better preventive measures are required to reduce morbidity among vulnerable populations.