Seasonal Variation in Incidence of Stroke in a General Population of 1.4 Million Japanese: The Shiga Stroke Registry

Abstract

<b><i>Introduction:</i></b> The purpose of this study was to investigate seasonal variation in stroke incidence using data from a large-scale stroke registry of general population in current Japan. <b><i>Methods:</i></b> Shiga Stroke Registry (SSR) is an ongoing population-based registry of stroke that occurred in the Shiga Prefecture in central Honshu, Japan. A total 6,688 cases of first-ever stroke, with onset dates ranging from 1 January 2011 to 31 December in 2013 were included in this study. Incidence rates of first-ever stroke in each season were estimated using the person-year approach and adjusted for age and sex using the Poisson regression models. <b><i>Results:</i></b> From 2011 to 2013, we identified a total of 6,688 stroke cases (3,570 men, 3,118 women), of which 4,480 cases had ischemic stroke (2,518 men, 1,962 women), 1,588 had intracerebral hemorrhage (857 men, 731 women) and 563 had subarachnoid hemorrhage (166 men, 397 women). Age- and sex-adjusted incidence rates of total stroke were 151 (95% confidence interval [CI] 144–160, <i>p</i> = &#x3c;0.001 vs. summer) in spring, 130 (95% CI 122–137) in summer, 141 (95% CI 133–149, <i>p</i> = 0.020 vs. summer) in autumn and 170 (95% CI 161–179, <i>p</i> = &#x3c;0.001 vs. summer) in winter. Seasonal variation was more pronounced in intracerebral hemorrhage than in ischemic stroke. <b><i>Conclusion:</i></b> In the present large-scale stroke registry of general population, incidence rates of stroke were highest in winter and lowest in summer in current Japan.