Incidence But Not Severity of Intracerebral Hemorrhage Shows a Strong Pattern of Seasonal Variation.

Abstract

Background: A strong risk factor for intracerebral hemorrhage (ICH) is elevated arterial blood pressure, which is known to vary by season, with highest values in winter months. The objective was to assess seasonal trends of ICH incidence, clinical severity, and case fatality according to demographic and clinical characteristics.

Methods: This study was conducted on adult patients hospitalized for ICH between 2003 and 2022. Cases were identified from a stroke inpatient quality assurance registry covering the entire Federal State of Hesse, Germany. Population data were derived from the Hessian Bureau of Statistics. Incidence rates (IRs) per 100 000 person-years of ICH, recorded with 4-digit International Statistical Classification of Diseases, Tenth Revision, German Modification (ICD-10-GM) I61.x codes, were estimated by season, calendar month, and bleeding location. Seasonal variations and subgroup analyses were tested using Poisson distribution and the Wald test.

Results: A total of 33 444 patients were included (mean age, 72.4±13.6 years, 52% men). ICH IR correlated with the season of occurrence, demonstrating a peak in winter (IR winter, 34.6 [95% CI, 33.9-35.4], IR summer, 29.4 [95% CI, 28.7-30.1]; P<0.01). Seasonal variation was equally present in men and women but was more pronounced in older compared with younger patients (peak at age 60-90 years; P<0.01). IR showed seasonal variation both for cortical and subcortical bleeding locations (P<0.01). Clinical severity and case fatality did not vary between seasons (mean, 24.3±0.8%).

Conclusions: This large cohort study demonstrates a seasonal incidence peak of ICH in winter. Whether ICH can be prevented by better control of arterial blood pressure in seasons with expected incidence peaks will require further studies.