Seasonal variation in stroke in the Hunter Region, Australia: a 5-year hospital-based study, 1995-2000

Background and Purpose: Seasonal variation in stroke has long been recognized. To date, there are minimal published data on seasonal variations in rates of stroke and subsequent case fatality in the Southern Hemisphere. The aim of this study was to examine stroke seasonality through the use of data from a hospital-based stroke register in the Hunter Region of New South Wales, Australia. Methods: From July 1, 1995, to June 30, 2000, 3803 stroke events were registered in residents of the Hunter Region, New South Wales, Australia. We analyzed the trend of seasonal and monthly stroke attack rates and case-fatality rates using Poisson regressions with age and sex as covariates. Results: Stroke attack rates were highest in the winter and lowest in the summer. From February (summer) to July (winter), there was a significant trend in increasing stroke attack rates (rate ratio, 1.07; 95% confidence interval, 1.05 to 1.10;P <0.001). This increase was seen mainly in those >=65 years of age. Case-fatality rates showed similar trends with a 1- to 2-month lag compared with attack rates. Conclusions: There is an increase in stroke attack rates and case-fatality rate from summer to winter in the Hunter Region, Australia. These trends are similar to those found in the Northern Hemisphere.