Short-term exposure to fine particulate matter —
the microscopic particles that pollute the air —
increased hospital admissions for cardiovascular and
respiratory disease among Medicare participants, according
to a study of 204 urban counties in the United States
conducted by researchers at the Johns Hopkins
Bloomberg School of Public
Health and the Yale University School of Forestry and
Environmental Studies. In 2002, for every 10 micrograms per
cubic meter increase in particulate matter, the researchers
calculated 11,000 additional cardiovascular and respiratory
disease hospitalizations. Increased risk for cardiovascular
disease hospitalizations, as a result of increased levels
of particulate matter, was highest in counties located in
the eastern United States. The study authors created a
reproducible approach for tracking the health risks of air
pollution nationwide. The study is published in the March 8
edition of the Journal of the American Medical
Association.
Particulate matter is an airborne mixture of solid
particles and liquid droplets. The solid particles come in
numerous shapes and sizes and may be composed of different
chemical components. Fine particles, defined as 2.5
micrometers or less in size (approximately 1/30th the
diameter of a human hair), can penetrate deep into the
body's respiratory system. Airborne particles come from a
variety of sources, including coal-burning power plants,
factories, automobiles, tilled fields, the crushing of
stone and the burning of wood. Other particles may be
formed in the air when sunlight and water vapor react with
gases emitted from burning fuels.
"By linking geographical locations and the health
information of roughly all Medicare enrollees to the
national air pollution and weather monitoring network, and
to the U.S. census data, we can now routinely estimate
health effects of air pollution nationally and regionally,"
said the study's lead author, Francesca Dominici, associate
professor in the
Department of Biostatistics at the Bloomberg School.
The researchers estimated associations between
day-to-day changes in hospital admission rates for
cardiovascular and respiratory outcomes (heart failure,
heart rhythm disturbances, cerebrovascular events,
peripheral vascular disease, ischemic heart disease,
chronic obstructive pulmonary disease and respiratory
infection) as compared to fine particulate matter levels
for 204 U.S. urban counties from 1999 to 2002. The study
included 11.5 million Medicare enrollees who lived, on
average, 5.9 miles from fine particulate matter monitors.
The study authors used same-day hospitalizations for
injuries as control measurements.
Dominici and her colleagues found that a 10 microgram
per cubic meter increase in particulate matter was
associated with a 1.28 percent increase in the risk of
admission for heart failure. Cook County, Ill., which
includes Chicago, can be used as an example. The area has
an annual average fine particle level of 16 micrograms per
cubic meter and a high level of 56 micrograms per cubic
meter. For each 100 hospital admissions for heart failure,
the study results showed approximately one extra hospital
admission associated with each 10 microgram per cubic meter
daily fine particulate matter increase. Therefore, on days
with the highest fine particle levels, the study results
predicted five extra hospital admissions for each 100
hospital admissions.
The oldest group of study participants also
experienced higher risks of ischemic heart disease, heart
rhythm disturbances, heart failure and chronic obstructive
pulmonary disease associated with high particulate matter
level days. As expected, the researchers did not find any
association between levels of fine particulate matter and
injuries.
"Our study makes available all of the relevant
material, software and methodology that support the
principal findings. Reproducibility is critical for large
studies with significant implications such as this one,"
said co-author Roger D. Peng, an assistant professor in the
Bloomberg School's Statistics Department and an advocate
for making research reproducible by others.
Previously, researchers at the Bloomberg School
reported an association between particulate matter levels
and mortality nationwide. Other research studies at the
school showed associations between particulate matter and
premature death from cardiopulmonary causes,
hospitalization for respiratory or cardiovascular diseases
and exacerbation of respiratory diseases.
Jonathan M. Samet, senior author of the study and
chair of the Bloomberg School's Department of Epidemiology,
said, "This study shows an ongoing threat to health from
airborne particles. The sources of particles contributing
to the observed risks need to be identified so that control
strategies can be targeted efficiently. Research is
shifting toward the difficult task of identifying the
characteristics of particles that determine their
toxicity."
Samet, Dominici and colleagues last month received an
$8 million Science to Achieve Results grant from the U.S.
Environmental Protection Agency to establish a new center
at the Bloomberg School to study the health effects of
particulate matter.
Additional study authors from Johns Hopkins are Luu
Pham, Aidan McDermott and Scott L. Zeger. Michelle L. Bell,
of Yale, also co-authored the study.
The study was supported by grants from the U.S.
Environmental Protection Agency, the National Institute for
Environmental Health, the NIEHS Center in Urban
Environmental Health and the Health Effects Institute
through a Walter A. Rosenblith New Investigator Award.