Reconstruction of pseudonymized patient-trajectories in Austria's stroke cohort using medical record-linkage of in-patient routine documentation to establish a nation-wide acute stroke cohort of 102,107 pseudonymized patients between 2015 and 2019.

Introduction: Administrative health data are increasingly used for disease surveillance, quality assurance and research purposes. In Austria, reporting of a standardized dataset is mandatory for each patient.

Patients And Methods: Routine documentation includes administrative and medical data, including admission and discharge characteristics, disease-diagnosis using ICD-10, medical procedure codes, and coding of involved hospital departments. Since 2015, a three-step pseudonymization on these data is provided including a pseudonym using secure hash algorithm 256, a non-recalculable record-ID, and age-groups of 5 years, allowing the reconstruction of individual patient-trajectories. We included persons aged ⩾20 years with an in-patient treatment in Austrian hospitals for acute stroke or transient ischemic attack (TIA) between 01.01.2015 and 31.12.2019 using medical record-linkage.

Results: This totals 102,107 patients (49.3% women) with 107,055 treatment episodes. An ischemic stroke (IS) occurred in 60.9% ( = 65,133), 27.1% ( = 29,019) had a TIA, 3.3% ( = 3488) a subarachnoid hemorrhage, and 8.8% ( = 9415) an intracerebral hemorrhage (ICH). The study period covers 35.2 million person-years at risk, with a hospitalization rate for acute stroke of 221.8 per 100,000 person-years (95% CI 220.2-223.3), and 185.1 per 100,000 person-years (95% CI 183.7-186.5) for IS. Unscheduled re-admissions within 1 year occurred in 29.2% (95% CI 28.8-29.7) after IS, and 41.7% (95% CI 40.0-43.3) after ICH. Recurrent stroke occurred in 5.3% (95% CI 5.1-5.5) after IS, and 5.6% (95% CI 4.9-6.4) after ICH.

Discussion: We present herein the details of a novel methodology to establish a nation-wide unselected Austrian stroke cohort, and to reconstruct pseudonymized individual longitudinal patient-trajectories on a national level. This approach shows potential applications in epidemiological research, quality assessment and outcome measurement.

Conclusion: This novel approach opens new research fields, facilitates international comparison, and is needed for national benchmarking to assess the achievement of goals according to the Stroke Action Plan for Europe and augment the quality of Austria's integrated stroke care.