Wang HC, Yousef E. J Asthma. 2007;44(10):839–841
PURPOSE OF THE STUDY. To examine the effects of seasonality, outdoor air quality, climatic factors, and presence of outdoor aeroallergens on emergency department (ED) visits for children with asthma.
STUDY POPULATION. Dates with “low” and “high” pediatric ED visits with a primary diagnosis of asthma (International Classification of Diseases, Ninth Revision code 493) were identified for children presenting to Alfred I. du Pont Hospital for Children from January 1, 2000, to December 31, 2003. Dates with zero ED visits for asthma were labeled as low, and dates with ≥7 ED visits for asthma were labeled as high.
METHODS. This was a retrospective review of ED visits for asthma and environmental factors, with 8-hour average ozone, 24-hour average nitrogen dioxide (NO2), and particulate matter with an aerodynamic diameter of <2.5 μm (PM2.5) levels, as well as tree pollen, weed pollen, grass pollen, and mold levels obtained. Monthly minimum, maximum, and mean temperatures and precipitation levels were obtained. Seasonal and environmental factors associated with high and low ED visits for asthma were compared with independent t tests.
RESULTS. Of 1460 dates reviewed over a 4-year period, 106 were classified as low-visit days and 103 were classified as high-visit days. Of high-visit days, 45.6% were in autumn, 28.2% were in spring, 14.6% were in winter, and 11.7% were in summer. The greatest proportion of high-visit days occurred in September. Mean 8-hour average ozone for low-visit days was significantly higher than on high-visit days (0.047 vs 0.033 ppm). No differences were observed in mean 24-hour average NO2 levels on high- and low-visit days. The mean 24-hour average PM2.5 was higher on low-visit days (18.54 μg/m3) versus high-visit days (13.28 μg/m3). Trends were observed with higher weed and tree pollen on high-visit days. Mean temperature and precipitation were both significantly lower on high-visit days.
CONCLUSIONS. Asthma-related ED visits were associated with aeroallergens and climactic factors. Air pollutants seem to play a smaller role in asthma-related ED visits.
REVIEWER COMMENTS. This retrospective analysis has identified significant seasonal variation in high and low ED visits for pediatric asthma. The results suggest that the observed seasonal variation may be related to weed- and tree-pollen levels and climactic factors. However, the study may have been inadequately powered to identify minor differences between the high- and low-visit groups. Air pollutant levels were not associated with asthma-related ED visits in the expected direction (low-visit days had higher pollutant levels). Perhaps there is a delayed effect of air pollutant exposure that was not identified by the study methodology. Results from multiple comparisons were not presented, but interaction effects are feasible. Another limitation is that the use of International Classification of Diseases, Ninth Revision codes to identify visits is subject to misclassification. Prospective studies that include daily maximum ozone levels and patient-level data on susceptibility to exposures of interest could better inform the environmental impact on ED visits for childhood asthma.
- Copyright © 2008 by the American Academy of Pediatrics