Objective: To investigate the extent to which the incidence and mortality of a first-time stroke among younger and older adults changed from 2005 to 2018 in Denmark using nationwide registries.

Methods: We used the Danish Stroke Registry and the Danish National Patient Registry to identify patients aged 18–49 years (younger adults) and those aged 50+ years (older adults) with a first-time ischemic stroke, intracerebral hemorrhage, or subarachnoid hemorrhage. We computed age-standardized incidence rates and 30-day and one-year mortality risks separately for younger and older adults and according to smaller age groups, stroke subtype, sex, and severity (Scandinavian Stroke Scale). Average annual percentage changes (AAPC) were computed to assess temporal trends.

Results: We identified 8,680 younger adults and 105,240 older adults with an ischemic stroke or intracerebral hemorrhage. The incidence rate per 100,000 person-years of ischemic stroke (20.8 in 2005 and 21.9 in 2018, AAPC: -0.6 [95% CI: -1.5 to 0.3]) and intracerebral hemorrhage (2.2 in 2005 and 2.5 in 2018, AAPC: 0.6 [95% CI: -1.0 to 2.3]) remained steady in younger adults. In older adults, rates of ischemic stroke and intracerebral hemorrhage declined, particularly in those aged 70 or older. Rates of subarachnoid hemorrhage declined, but more so in younger than older adults. Stroke mortality declined over time in both age groups, largely attributable to declines in the mortality after severe strokes. Most trends were similar for men and women.

Conclusion: Incidence of ischemic stroke and intracerebral hemorrhage was steady in younger adults from 2005 to 2018, while it dropped in adults older than 70 years. Stroke mortality declined during this time.

eTable 1. Description of the data sources used in this study.

eTable 2. International Classification of Diseases (ICD) and Anatomical Therapeutic Chemical Classification System (ATC) codes used in the study.

eTable 3. Characteristics (N, %) of patients with a first-time subarachnoid hemorrhage, Denmark, 2005–2018.

eTable 4. Number of Joinpoints and corresponding Joinpoints segments, annual percent change (APC), and average annual percent change (AAPC) for age- and sex-specific incidence rates of ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage, 2005–2018.

eTable 5. Number of Joinpoints and corresponding Joinpoints segments, annual percent change (APC), and average annual percent change (AAPC) for age-, severity-, and etiology-specific incidence rates of ischemic stroke and intracerebral hemorrhage, 2005–2018.

eTable 6. Number of Joinpoints and corresponding Joinpoints segments, annual percent change (APC), and average annual percent change (AAPC) for age- and sex-specific 30-day and 1-year mortality risks of ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage, 2005–2018.

eTable 7. Number of Joinpoints and corresponding Joinpoints segments, annual percent change (APC), and average annual percent change (AAPC) for age- and severity-specific 30-day and 1-year mortality risks of ischemic stroke and intracerebral hemorrhage, 2005–2018.

eFigure 1. Age-standardized incidence rates with corresponding 95% confidence intervals of a first-time ischemic stroke or unspecified stroke (specific codes) in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 2. Age- and etiology-specific incidence rates with corresponding 95% confidence intervals of a first-time ischemic stroke (atrial fibrillation associated, rare risk factor associated, others) or intracerebral hemorrhage (hypertension associated, anticoagulation associated, others) in younger and older adults, 2005–2018. Atrial fibrillation diagnoses identified during hospitalization or within the following 180 days. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 3. Age-specific 1-year mortality risks and corresponding 95% confidence intervals following a first-time ischemic stroke or intracerebral hemorrhage in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 4. Age- and sex-specific 30-day mortality risks and corresponding 95% confidence intervals following a first-time ischemic stroke or intracerebral hemorrhage in younger and older adults. Dotted lines represent women; solid lines represent men), 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 5. Age-standardized and severity-specific 30-day mortality risks and corresponding 95% confidence intervals of a first-time ischemic stroke or intracerebral hemorrhage in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 6. Age-standardized and severity-specific 1-year mortality risks and corresponding 95% confidence intervals of a first-time ischemic stroke or intracerebral hemorrhage in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 7. Age-specific 30-day mortality risks and corresponding 95% confidence intervals following a first-time subarachnoid hemorrhage in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.

eFigure 8. Age-specific 1-year mortality risks and corresponding 95% confidence intervals following a first-time subarachnoid hemorrhage in younger and older adults, 2005–2018. Fitted smoothed lines are Loess smoothers. Notice varying y-axes.