Link Found Between Coarse Particulate Matter Exposure and Pediatric Asthma

Corinne A. Keet, MD, PhD

Exposure to coarse particulate matter (PM) pollution may increase the prevalence of asthma in US children enrolled in Medicaid, according to a new study.

Lead author Corinne A. Keet, MD, PhD, Associate Professor at John Hopkins University School of Medicine, Division of Pediatric Allergy and Immunology, told MD Magazine that the most striking finding of the study was that PM levels — that is, large-sized particulate pollution — were independently associated with asthma prevalence and exacerbations.

“This is important because this type of pollution is not currently regulated and much less attention has been given to it,” Keet said.

Fine PM usually originates from combustion or reactions in the atmosphere, while coarse PM is created from grinding and resuspension of solid materials. Long and short-term exposure to fine PM has been extensively researched and found to be associated with asthma development. However, there is little data on the effects of long-term exposure to coarse PM, which is thought to be less harmful than fine PM because particle size limits penetration in the lungs. In the study, researchers note there is mounting evidence that short-term exposure to coarse PM may be associated with cardiovascular and respiratory morbidity.

There were 7.8 million US children aged 5 to 20 years enrolled in Medicaid between January 1, 2009 to December 31, 2010. Only children enrolled for the full 2-year period of the study were included. Medicaid data was obtained from the Research Data Assistance Center, collected and aggregated on the state level, then processed by the Centers for Medicare and Medicaid into the Medicaid Analytic Extract (MAX).

The following states were excluded from analysis: Maine, Pennsylvania, Ohio, Idaho, Arkansas, and Kansas, because of utilization data quality or had large inconsistencies in asthma care utilization between 2009 and 2010. Alaska and Hawaii were excluded because of the difficulty in predicting PM in the non-contiguous states. In addition, because previous research has shown that race/ethnicity is strongly associated with asthma prevalence, Colorado, Massachusetts, New Jersey Rhode Island, Vermont, Washington and Wisconsin were excluded because more than 10% percent of subjects had missing data for race/ethnicity.

A 1 mcg/m³ increase in average fine PM was associated with a 2.3% increase in the prevalence of diagnosed asthma (95% CI; 1.014-1.031; P < 0.001), 7.2% increase in asthma hospitalizations (95% CI; 1.042-1.102; P < 0.001), and 4.2% increase in Emergency Room (ER) visits (95% CI; 1.019-1.066; P < 0.001).

A coarse PM increase of 1 mcg/m³ was associated with a 1.1% increase of asthma prevalence (95% CI; 1.007-1.015; P < 0.001), 3.6% increase in asthma hospitalizations (95% CI; 1.018-1.053; P < 0.001), and 2.6% increase in ER visits (95% CI; 1.015-1.038; P < 0.001).

Study authors said that these associations were adjusted for exposure to fine PM and suggest that the asthma-related effects after exposure to coarse PM were independent of fine PM.

“Overall, we know that improvements in air quality and the Clean Air Act have improved respiratory health, but we still have a long way to go,” Keet said. “This study shows that the levels of coarse PM in the U.S. today are having an effect on children’s asthma.”

Keet said some of the many questions left to be researched include the regional differences in coarse PM pollution, the effects of different sources of coarse PM pollution, and the effects of short-term changes in coarse PM.

The study, "Long-term Coarse PM Exposure is Associated with Asthma Among Children in Medicaid," was published online in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

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