Background and objectives: In the field of stroke epidemiology, one of the major advances in the recently implemented International Classification of Diseases, 11th revision (ICD-11) relates to the definition of ischemic stroke, which now includes events shorter than 24 hours when ischemia can be proven on brain imaging. However, data are scarce to ascertain the incidence of strokes of short duration with tissue evidence of ischemia. In this study, we determined the incidence, 30-day case fatality, and mortality rate of stroke in the Geneva population using the new ICD-11 criteria, taking advantage of the organization of stroke service in the area.

Methods: In this population-based observational cohort study, we used data from the Swiss Stroke Registry, supplemented by hospital records, outpatient medical files, and autopsy, to identify residents of the canton of Geneva, Switzerland, meeting the ICD-11 criteria for first-ever stroke, including ischemic strokes, nontraumatic intracerebral hemorrhage (ICH), or subarachnoid hemorrhage (SAH), from January 1, 2018, to December 31, 2019.

Results: We identified 1,186 first-ever strokes (75.8 years [interquartile range 63.4-84.5]; 571 women [48.1%]). MRI was performed in 90.9% of patients with ischemic strokes. The annual incidence of first-ever stroke, age-adjusted to the European Standard Population, was 127.0/100,000 (95% CI 119.8-134.3) (107.3 [100.7-114.0] for ischemic stroke, 13.2 [10.9-15.5] for ICH, and 6.0 [4.4-7.5] for SAH [3.1 {2.0-4.2} for aneurysmal SAH]). Overall, the 30-day case fatality was higher in ICH (32.5% [95% CI 19.7-38.8], compared with SAH (17.2% [6.6-27.9] and ischemic strokes 10.8% [8.4-12.4]). The incidence of ischemic stroke was 107.3 (100.7-114.0) according to ICD-11 and 90.4 (84.3-96.5) according to ICD-10 (excluding patients with radiologic infarct and symptoms lasting <24 hours). Compared with ICD-10, ICD-11 increased the number of ischemic stroke cases by 18.3%. Patients with ischemic strokes identified with ICD-11 but not under ICD-10 (i.e., patients with symptoms lasting <24 hours and a brain lesion) were younger and presented with a lower National Institutes of Health Stroke Scale (NIHSS) score on admission compared with those identified by ICD-10 and ICD-11.

Discussion: The new ICD-11 clinicoradiologic definition of ischemic stroke increased the number of ischemic stroke cases by 18.3% in our Western European population. Future studies will evaluate the impact of ICD-11 on the human, organizational, and economic needs allocated to the management of the disease.