Study objective: Asthma morbidity is greater in younger patients. The reasons are not fully understood, although identifying demographic patterns of seasonality may help determine causes and potential prevention. The objective of this study is to determine the relationship between age and seasonal asthma periodicity in patients presenting to the emergency department (ED).
Methods: We conducted a retrospective study of ED visits from 1991 to 2000 in 11 municipal hospitals in New York City, with 911 receiving facilities. There were 673,141 patients who presented to the ED during the study period and had a primary diagnosis of acute asthma.
Results: Distinct seasonal patterns were observed, with the highest number of visits occurring in the fall and the fewest in the summer. Seasonal fluctuations of ED visits were highest in children aged 13 years or younger (coefficient of variation [CV] 37.8%; 95% confidence interval [CI] 37.5% to 38.1%), with a peak in CV occurring at approximately age 7 years (CV 43.3%; 95% CI 43.0% to 43.6%). Less variability was noted with increasing age, and the population aged 30 years and older appeared to be the least susceptible to seasonal influences (CV 11.7%; 95% CI 11.3% to 12.1%). Although the total number of asthma visits decreased by more than 30% from 1991 to 2000, the CVs for each year remained within a relatively narrow range of 24.2% to 30.5%.
Conclusion: In an urban population, seasonal variability of asthma episodes requiring ED visits are closely linked to age, which may be important in understanding the causes of asthma and developing disease-management strategies for the prevention of asthma episodes.