Asthma and the Brisbane Climate

Summary: An analysis of 3,992 night attendances for asthma at the Royal Brisbane Hospital Casualty Department for the ten years 1959–1968 showed seasonal, annual and short‐term variations. Each year a major wave of asthma attendances began in autumn and a minor wave in spring. In the average year the autumn wave extended from mid‐March to the end of July, with its crest from late April to late May. The spring wave extended from early in October until early in January, with a peak toward the end of October. In individual years the waves varied considerably in timing, magnitude and pattern. Attendances were minimal in January‐March and August‐September. Seasonal variation diminished with increasing age. The relation of asthma to the weather was complex. Maximal attendances occurred when the mean ambient temperature was about 21°C (70°F) and the dew point about 13.5°C (56°F). Attendances decreased as temperature or dew point rose above or fell below these levels. In the 26 cooler weeks of the average year, the weekly asthma attendances showed highly significant positive correlation (P < 0.001) with the mean temperature, dew point and 3 pm relative humidity; the greatest correlation was with the measurements of these elements five to six weeks earlier. There was also highly significant correlation (positive) with rainfall and soil moisture, greatest with a lag of 16 weeks, and (negative) with hours of sunshine with no lag. In the 26 warmer weeks, weekly attendances became significantly fewer the higher the temperature, dew point, relative humidity, rainfall and soil moisture of the same weeks. Variation from year to year in the amount of asthma in autumn showed significant correlation (P <0.01 or < 0.05) with variation in dew point and rainfall (positive) and sunshine (negative), that in spring with variation in temperature and dew point (positive). In each season correlations were greatest when asthma was compared with the weather several weeks earlier. Two short‐term relationships of asthma to the weather have been demonstrated. (A) Cold dry changes were frequently accompanied by an increase in asthma. Suggested mechanisms include a direct effect of cold on susceptible subjects and the liberation of allergens into the air in dry weather. The crest of the autumn wave commonly occurred while the weekly temperature was falling most steeply. (B) During rainy periods asthma usually decreased, probably from a reduction in airborne allergens. On the evidence presented here it is not possible to explain fully the aetiology of autumn and spring asthma in terms of house‐dust mites, fungal spores or pollens, although each of these contributes to them, or air pollution. An increase of asthma some weeks after warm wet weather suggests the production of important allergens not yet identified. Fungal spores especially deserve further investigation. It is probable that different allergens predominate in autumn and spring. Further investigations are called for to determine the factors that make asthma highly prevalent in areas such as Brisbane, Durban and New Orleans. It is noteworthy that these places have a mean annual temperature of 20–22°C (68–72°F) and an average annual rainfall of over 100 cm (40 inches).