Time trends in incidence, comorbidity, and mortality of ischemic stroke in Denmark, 1996-2016

OBJECTIVE: To examine whether the incidence, comorbidity, and mortality of first-time ischemic stroke changed in Denmark between 1996 and 2016 overall and according to age and sex using a nationwide cohort design.

METHODS: In this cohort study, 224,617 individuals ≥18 years of age admitted with first-time ischemic stroke between 1996 and 2016 were identified through Danish nationwide registries. We calculated annual age-standardized incidence rates and absolute 30-day and 1-year mortality risks. Furthermore, we calculated annual incidence rate ratios using Poisson regression, odds ratios for 30-day mortality using logistic regression, and hazard ratios for 1-year mortality using Cox regression.

RESULTS: The overall age-standardized incidence rates of ischemic stroke per 1,000 person-years increased from 1996 (2.70 [95% confidence interval [CI] 2.65-2.76]) to 2002 (3.25 [95% CI 3.20-3.31]) and then gradually decreased to below the initial level until 2016 (1.99 [95% CI 1.95-2.02]). Men had higher incidence rates than women in all age groups except 18 to 34 and ≥85 years. Absolute mortality risk decreased between 1996 and 2016 (30-day mortality from 17.1% to 7.6% and 1-year mortality from 30.9% to 17.3%). Women between 55 and 64 and ≥85 years of age had higher mortality than men. Similar trends were observed for all analyses after multivariable adjustment. The prevalence of atrial fibrillation, hypertension, diabetes mellitus, and use of lipid-lowering medication increased during the study period.

CONCLUSIONS: The age-standardized incidence of first-time hospitalization for ischemic stroke increased from 1996 to 2002 and then gradually decreased to below the initial level until 2016. Absolute 30-day and 1-year mortality risks decreased between 1996 and 2016. These findings correspond to increased stroke prevention awareness and introduction of new treatments during the study period.