Introduction: Seasonal variation in asthma has been widely recognized. The aim of this study was to describe seasonal patterns of asthma symptoms and asthma medication use in a cohort of pediatric asthma medication users and to study determinants of seasonal childhood asthma.
Methods: For this study, 602 children participating in the Pharmacogenetics of Asthma medication in Children: Medication with Anti-inflammatory effects) cohort were included. Parents were asked about their child's respiratory symptoms and quick-reliever medication use over the past year. Logistic regression analysis was used to study determinants of seasonality in asthma control (the level of disease control based on symptoms, limitations in activities, and rescue medication use).
Results: There was a decline in asthma symptoms and asthma medication use during the summer period and a peak occurred from autumn to spring. The prevalence of wheeze ranged from 32% in summer to 56% in autumn. The prevalence of respiratory symptoms and medication use was significantly lower during summer (p < .0001). Oral steroids and antibiotics use and strong parental necessity beliefs were associated with uncontrolled asthma, regardless of seasonality. Allergic rhinitis was associated with an increased risk of uncontrolled asthma during spring [odds ratio (OR): 1.9; 95% confidence interval (CI): 1.3-2.8] and summer (OR: 1.9; 95% CI: 1.2-3.0). Eczema was associated with a higher risk of uncontrolled asthma during autumn (OR: 1.5; 95% CI: 1.0-2.2) and winter (OR: 1.3; 95% CI: 1.0-1.9).
Conclusion: We showed seasonal patterns in asthma symptoms and medication use. Associations were shown between allergic rhinitis and asthma control during spring/summer and eczema was associated with uncontrolled asthma during autumn/winter. Seasonality in asthma morbidity and health-care use is most likely associated with atopic constitution and viral infections, which are common during fall, winter, and spring.