Background: There are few large population-based studies of outcomes after subarachnoid hemorrhage (SAH) than other stroke types.

Methods: We pooled data from 13 population-based stroke incidence studies (10 studies from the INternational STRroke oUtComes sTudy (INSTRUCT) and 3 new studies; N=657). Primary outcomes were case-fatality and functional outcome (modified Rankin scale score 3-5 [poor] vs. 0-2 [good]). Harmonized patient-level factors included age, sex, health behaviours (e.g. current smoking at baseline), comorbidities (e.g.history of hypertension), baseline stroke severity (e.g. NIHSS >7) and year of stroke. We estimated predictors of case-fatality and functional outcome using Poisson regression and generalized estimating equations using log-binomial models respectively at multiple timepoints.

Results: Case-fatality rate was 33% at 1 month, 43% at 1 year, and 47% at 5 years. Poor functional outcome was present in 27% of survivors at 1 month and 15% at 1 year. In multivariable analysis, predictors of death at 1-month were age (per decade increase MRR 1.14 [1.07-1.22]) and SAH severity (MRR 1.87 [1.50-2.33]); at 1 year were age (MRR 1.53 [1.34-1.56]), current smoking (MRR 1.82 [1.20-2.72]) and SAH severity (MRR 3.00 [2.06-4.33]) and; at 5 years were age (MRR 1.63 [1.45-1.84]), current smoking (MRR 2.29 [1.54-3.46]) and severity of SAH (MRR 2.10 [1.44-3.05]). Predictors of poor functional outcome at 1 month were age (per decade increase RR 1.32 [1.11-1.56]) and SAH severity (RR 1.85 [1.06-3.23]), and SAH severity (RR 7.09 [3.17-15.85]) at 1 year.

Conclusion: Although age is a non-modifiable risk factor for poor outcomes after SAH, however, severity of SAH and smoking are potential targets to improve the outcomes.