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Higher Concentrations of Outdoor Particulate Matter Are Associated With Increased Severe Asthma Exacerbations


  • Do children with mild-to-moderate asthma have more severe asthma attacks when exposed to higher concentrations of pollution in the air?

Clinical Bottom Lines

  1. There is a statistically significant correlation between severe asthma attacks and increased amounts of particulate matter in the air.
  2. Smaller diameter particles result in more severe asthma attacks than do larger particles.
  3. This study is an epidemiologic study following a cohort of children; therefore NNT could not be calculated, and influence on clinical practice could not be assessed.

Summary of Key Evidence

  1. Children with mild-to-moderate asthma have a 1.20 increased odds of severe asthma attacks when particulate matter of 2.5 microns in diameter is increased by 10 g/m3. The same children have a 1.10 increased odds of having a severe asthma attack when larger particulate matter (diameter of 10 microns) is increased by the same amount. These results are statistically significant.1
  2. The patient population included children ages 5-13 years, with mild-to-moderate asthma, not on controller meds, in the Seattle area.
  3. Severe asthma attacks were defined as those lasting more than two hours, resulting in shortened normal activity, or requiring acute care by a physician.
  4. Air pollution data was obtained from multiple air pollution monitoring stations as maintained by the Puget Sound Clean Air Agency.
  5. There is a weaker association between increased particulate matter and number of rescue inhaler puffs used. There is also an association between increased levels of CO and increased attacks and inhaler use, but CO levels may be a surrogate marker for exposure to particulate matter.

Additional Comments

  • Increased amounts of particulate matter are associated with motor vehicle exhaust fumes, incinerators, and other combustive processes.2
  • There has long been a recognized association between increased symptom severity, visits to emergency rooms, and mortality in patients with chronic lung disease, when larger diameter particulate matter in increased.2 This paper examines the association between smaller diameter particulate matter and severe asthma symptoms.1,2
  • The proposed biologic mechanism is the induction of inflammation by the deposition of particulate matter in the altered airways of patients with asthma.2,3
  • This is an epidemiologic study; therefore, it is not randomized, there is no control group, and there is potential for confounders not identified in the analysis (e.g. indoor allergens).3


  1. Slaughter JC et. al. Effects of ambient air pollution on symptom severity and medication use in children with asthma. Ann Allergy Asthma & Imm 2003; 91: 346-353.
  2. Slavi S. Ambient particulate air pollution and childhood asthma exacerbations (editorial). Ann Allergy Asthma & Imm 2003; 91:321-323.
  3. Etzel R. How environmental exposures influence the development and exacerbation of asthma. Pediatrics 2003; 112: 233-239.

CAT Author: Jennifer Janus, MD

CAT Appraisers: Robert Schumacher, MD

Date appraised: December 22, 2003

Last updated October 27, 2004
Department of Pediatrics and Communicable Diseases
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