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The relationship of respiratory and cardiovascular hospital admissions to the southern California wildfires of 2003
  1. R J Delfino1,
  2. S Brummel2,
  3. J Wu1,3,
  4. H Stern2,
  5. B Ostro4,
  6. M Lipsett5,
  7. A Winer6,
  8. D H Street7,
  9. L Zhang5,
  10. T Tjoa1,
  11. D L Gillen2
  1. 1
    Department of Epidemiology, School of Medicine, University of California, Irvine, California, USA
  2. 2
    Department of Statistics, School of Information and Computer Science, University of California, Irvine, California, USA
  3. 3
    Program in Public Health, University of California, Irvine, California, USA
  4. 4
    Air Pollution Epidemiology Section, California Office of Environmental Health Hazard Assessment, Oakland, California, USA
  5. 5
    Exposure Assessment Section, Environmental Health Investigations Branch, California Department of Health Services, Oakland, California, USA
  6. 6
    Department of Environmental Health Sciences, School of Public Health, University of California, Los Angeles, California, USA
  7. 7
    Independent consultant, Salem, Oregon, USA
  1. Dr Ralph J Delfino, Epidemiology Department, School of Medicine, University of California, Irvine, 100 Theory Dr., Suite 100, Irvine, CA 92617-7555, USA; rdelfino{at}


Objective: There is limited information on the public health impact of wildfires. The relationship of cardiorespiratory hospital admissions (n = 40 856) to wildfire-related 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 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% 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 −0.5% 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 μg/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 −1.0% 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.

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  • ▸ Additional information is published online only at

  • Funding: This study was funded by the South Coast Air Quality Management District contract no. 04182, and the National Institutes of Health, National Institute of Environmental Health Sciences grant no. ES-11615.

  • Competing interests: None.