Seasonal variation of hospital admissions caused by acute stroke in Athens, Greece.

Several studies have reported a seasonal variation in stroke incidence with a peak during winter. In a hospital-based study, we investigated the distribution pattern of stroke occurrence in general, as well as its subtypes throughout the year. We studied the monthly and seasonal distribution of acute stroke occurrence among 1299 first ever stroke patients admitted at our hospital and compared it with the assumed equal distribution of stroke over the year (null hypothesis) using chi2 techniques. The seasonal distribution of the different stroke subtypes was also examined. Overall stroke incidence shows a seasonal variation with a significant peak during wintertime. Stroke etiology, cardioembolic stroke, and intracerebral hemorrhage are also characterized from a similar seasonal fluctuation with a significant trough in summer and peak in winter. On the contrary, cases of stroke caused by atherosclerotic large vessel disease, small vessel disease, and stroke caused by unusual or undetermined types show no seasonal periodicity. Seasonal variation of stroke seems to depend primarily on the etiology of stroke. Further studies are necessary in order to clarify this issue and provide useful evidence for stroke prevention and therapy.