Seasonal patterns of asthma: a clue to etiology

An extensive data set of daily hospital emergency room visits for asthma for two geographic areas (1953-77 in New Orleans and 1969-77 in New York City) was examined for seasonality. Previous studies using smaller data bases have reported an autumn increase (principally during October and November) in the number of emergency room visits for asthma in many locations in this country (including New Orleans and New York City). The results of this study indicated that for every hospital and every year of observation in New York City the number of asthma emergency room visits increased in September, reached a peak in October and November and declined in December. In contrast, in New Orleans an autumn increase in the number of asthma emergency room visits was not consistently observed, being absent or reduced during many years. The distribution of asthma epidemic days (days on which the number of asthma emergency room visits was greatly elevated) by month was also examined. In New York City, there was a tendency for these days to occur during September, October, and November while in New Orleans there was an equal likelihood of epidemic days occurring in April, May, and June as well as during September, October, and November. The observations tend to suggest different etiologies for asthma attacks in the two geographic areas.