Abstract WP228: Seasonal Variation of Stroke Subtypes Incidence in Population-based Study in Shiga Prefecture, Japan

Abstract

Introducution: Incidence rates of stroke have been shown to have seasonal variations. However, current evidence is limited for Japanese populations. The aim of this study was to investigate seasonal variation in incidence of stroke and its subtypes in a general population of 1.4 million Japanese. Methods: Shiga Stroke Registry is an ongoing population-based registry of stroke, which covers approximately 1.4 million residents of the Shiga prefecture in central Japan (located central part of Honshu Island). There is an integrated surveillance system involving the registration of cases among a network of all acute care hospitals with neurology/neurosurgery facilities and smaller hospitals with rehabilitation facilities. A total of 2,753 adult (18 years) cases of stroke (1838 ischemic stroke,713 intracerebral hemorrhage,196 subarachnoid hemorrhage and 6 other/unclassified), who were registered in 2011, were included in the present analysis. Incidence of stroke in each month of the year was estimated using 2011 vital statistics by a Poisson regression model with adjustment for age and gender. Results: The age- and gender-adjusted incidence rates of total stroke were 180, 176, 177, 162, 163, 149, 134, 128, 133, 152, 144, 177per 100,000 person-years from January to December, respectively. Incidence rates in summer were lower in summer (July to September) than those in winter (December to February) or spring (March to May). Similar patterns were also observed for both ischemic stroke and intracerebral hemorrhage although seasonal variation was much more remarkable for intracerebral hemorrhage.There were no clear differences between summer and winter for incidence rates of subarachnoid hemorrhage. Conlusions: Incidence rates of ischemic stroke and intracerebral hemorrhage seem to be high in winter and spring based on large-scale population-based stroke registry in Japan.