RESPIRATORY-INFECTIONS AND THE AUTUMN INCREASE IN ASTHMA MORBIDITY

Unexplained autumn increases in hospital admissions for asthma have be en reported in many countries, including the United States, Canada, En gland and Wales.To investigate the role of infection, the association was tested between hospital admissions for asthma and respiratory infe ctions among preschool children in Metropolitan Toronto, Canada during the period 1981 to 1989, The seasonal pattern in overall hospital uti lization was assessed by admissions for nonrespiratory diseases, Time series analysis was used to remove potentially confounding temporal tr ends and the influence of correlated errors. A fourfold increase in as thma admissions occurred between July and October unaccompanied by sim ilar increases in nonrespiratory admissions, Admissions began increasi ng during the third week of August, peaked during the third week in Se ptember, and slowly decreased during November and December, After adju sting for serial correlation, trends, climate, ambient air pollution a nd aeroallergens, the seasonal pattern of respiratory infection explai ned 14% of the variance in asthma admissions. Based on seasonal patter ns, respiratory infection is the major identifiable risk factor for th e large autumnal increase in asthma admissions.