Understanding the seasonal pattern of childhood asthma: results from the National Cooperative Inner-City Asthma Study (NCICAS)

OBJECTIVE: To contrast the seasonal patterns of asthma symptoms and utilization and determine the impact of allergen sensitivity, environmental tobacco smoke (ETS) exposure, and air pollution on the seasonal patterns of asthma. STUDY DESIGN: Participants in the National Cooperative Inner-City Asthma Study (NCICAS) were tracked for approximately 4 years after allergen skin testing and determination of exposure to ETS. Air pollution data were obtained from EPA monitoring sites in NCICAS cities. RESULTS: Asthma symptoms (wheeze) and health care utilization (unscheduled visits and hospitalization) had similar seasonal patterns, with low points during the summer months of June through August and a distinct autumn peak beginning in September. Seasonal patterns were similar among children with no allergen skin test reactivity, those reactive only to indoor allergens, and those reactive to outdoor allergens. ETS exposure, whether defined by self-report or urinary cotinine/creatinine ratio, was not related to the observed seasonal patterns. Among the pollutants evaluated, only the seasonal pattern of SO(2) coincided with that of asthma morbidity. CONCLUSIONS: Atopy, ETS, and most air pollutants do not appear to contribute to the distinct asthma seasonal pattern. On a population level, changes in symptoms are mirrored by changes in utilization.