Study Examines Relationship of Outdoor Air Quality and Asthma
Moderate Ozone Levels Not Implicated in Flareups
CINCINNATI -- The quality of outdoor air is commonly blamed for a host of detrimental effects on respiratory health. So why are there relatively few admissions for asthma to Cincinnati Children's Hospital Medical Center during the summer months, when air quality tends to be at its worst?
A new Cincinnati Children's study shows that high pollen counts are the most important predictor of admissions and emergency visits to Cincinnati Children's for asthma flare-ups. Air pollution in the form of tiny, airborne particles derived from car exhaust and industrial sources also contributes to asthma flare-ups. But another important air pollutant, ozone, does not cause asthma attacks severe enough to require hospital treatment, according to Michelle Lierl, MD, an allergist at Cincinnati Children's and the study's main author.
"Ozone, when present in high concentrations (greater than 12 parts per million of air), is irritating to the airways and can cause increased asthma symptoms," says Dr. Lierl, whose study is published in the January issue of Annals of Allergy, Asthma & Immunology. "Ozone concentrations in the moderate levels measured during this study, however, are not associated with pediatric asthma attacks severe enough to require hospital treatment. The highest ozone concentration recorded at the downtown Cincinnati monitoring station during the two years of this study was only 11 parts per million."
The study also showed that outdoor fungal (mold) spore counts were very high during the summer months but were not associated with an increased rate of asthma attacks.
The highest rates of asthma attacks requiring hospital visits occur during the spring and fall pollen seasons. Asthma attacks also occur frequently during winter, but the winter months were not included in this study since pollen, fungal spores and ozone are all very low during the winter. Winter asthma attacks are triggered mainly by viral respiratory infections and, in some cases, exposure to indoor allergens or tobacco smoke.
During the summer months, when ozone levels are highest, acute asthma attacks are relatively rare, presumably because of other factors, such as low community rates of respiratory infections and relatively low pollen counts.
"However, when lower pollen counts during the summer are combined with high levels of airborne pollution particulates, this combination of factors can trigger some asthma attacks," says Dr. Lierl. "During periods of poor outdoor air quality it is advisable for asthma patients to stay indoors."
To conduct the study, Dr. Lierl reviewed emergency department logs and patient records and obtained outdoor air data from the Hamilton County Department of Environmental Services. Because poor air quality does not always result in immediate hospital visits for asthma flare-ups, Dr. Lierl also tracked air quality measures from zero to five days before hospitalizations or emergency visits.
"The number of asthma visits per day was associated with the pollen count reported for the same day, but the effect became strongest for pollen counts reported three days before a visit," says Dr. Lierl.
Contact Information
Jim Feuer, 513-636-4656,
jim.feuer@cchmc.org
