Seasonal variations in hospital admissions and case-fatality of ischemic stroke: a nationwide analysis of >4.2 million cases in Germany

Background Ischemic stroke is a leading cause of global morbidity and mortality, with seasonal variations potentially influencing both outcomes. While previous studies have suggested a pronounced association of the cold months with increased stroke morbidity and mortality, the evidence remains limited and inconsistent. This study aimed to assess seasonal variations in ischemic stroke hospital admissions and in-hospital case-fatality and complications in Germany over an 18-year period. Methods This nationwide retrospective analysis included all hospitalizations for ischemic stroke in Germany from 2005 to 2022, using data from the Federal Statistical Office. Patients were categorized by season of hospital admission (winter, spring, summer, autumn). Multivariable logistic regression models were used to assess the association between season and in-hospital case-fatality, adjusting for age, sex, and comorbidities. Results A total of 4,236,789 ischemic stroke hospitalizations were analyzed. No statistically significant seasonal variation in stroke hospitalization was observed. However, in-hospital case-fatality was significantly higher in winter (7.4%) compared to summer (6.6%, p < 0.001). This seasonal association was independent of patient age, sex, and comorbidities [adjusted odds ratio (OR): 1.140, 95% confidence interval (CI): 1.128–1.152; p < 0.001]. Similar trends were observed in both men (adjusted OR: 1.122, 95% CI: 1.103–1.141; p < 0.001) and women (adjusted OR: 1.112, 95% CI: 1.096–1.128; p < 0.001), without substantial sex-specific differences. Conclusion While ischemic stroke hospital admissions remained stable across seasons, in-hospital case-fatality was significantly increased during winter compared to summer. These findings highlight the need for targeted seasonal prevention and management strategies. Further research is needed to explore underlying mechanisms and evaluate potential interventions to mitigate excess winter case-fatality among stroke patients.