Abstract TP121: Temporal Trends in Seasonal Variation of Frequency for Ischemic Stroke and Intracerebral Hemorrhage Admissions in a Nationwide Japanese Registry, 2005–2023

Introduction: Seasonal variation in stroke incidence has often been reported, but over the past two decades, climate and behavior have changed markedly, including global warming and COVID-19–related stay-at-home orders. We evaluated temporal trends in the seasonal distribution of hospital admissions for ischemic stroke and intracerebral hemorrhage (ICH) from 2005 to 2023. Methods: We analyzed patients in the Japan Stroke Data Bank, a multicenter prospective registry, from 2005 to 2023. We calculated seasonal proportions of admissions for ischemic stroke and ICH overall and by ischemic stroke subtype (large-artery atherosclerosis [LAA], cardioembolic [CE], and lacunar infarction). Seasons were defined as spring (March–May), summer (June–August), autumn (September–November), and winter (December–February). Seasonal distributions were summarized within four epochs (2005–2009, 2010–2014, 2015–2019, 2020–2023). Results: Overall, 228,127 cases were included. The ICH proportion was highest in winter (22.3%) and lowest in summer (17.5%) (p