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 (PM(2.5)) during catastrophic wildfires in southern California in October 2003
was evaluated.
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 250 m resolution. Generalised estimating equations
for Poisson data were used 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.
Associations of 2-day average PM(2.5) with respiratory admissions were stronger during
than before or after the fires. Average increases of 70 microg/m(3) 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 microg/m(3) PM(2.5), 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 PM(2.5)-asthma associations in children
ages 5-18 years, although their admission rates significantly increased after the
fires. Per 10 microg/m(3) wildfire-related PM(2.5), 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 PM(2.5) on cardiovascular admissions.
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.