Incidence of stroke in immigrants to Canada: a province-wide retrospective analysis

Objective — To evaluate the association between immigration status and stroke incidence.

Methods — We conducted a retrospective cohort study of 8 million adults (15% immigrants) residing in Ontario, Canada on January 1, 2003, with no history of prior stroke or transient ischemic attack (TIA). Subjects were followed until March 31, 2018 to identify incident stroke or TIA, defined as hospitalization or emergency room visit. We calculated adjusted hazard ratios (HR) of stroke or TIA in immigrants compared to long-term residents using cause-specific hazard models, adjusting for demographics and comorbidities. We evaluated whether the association varied by age, stroke type or country of origin of immigrants.

Results — During 109 million person-years follow-up, we observed 235,336 incident stroke or TIA events. Compared to long-term residents, immigrants had a lower rate of stroke or TIA (10.9 vs. 23.4 per 10,000 person-years, HR 0.67; 0.66-0.68). This was true across all age groups and stroke types, with a HR in immigrants vs. long-term residents for ischemic stroke of 0.71 (0.69-0.72), intracerebral hemorrhage 0.89 (0.85-0.93), subarachnoid hemorrhage 0.85 (0.81-0.91), and TIA 0.53 (0.51-0.54). The magnitude of the reduction in stroke risk associated with immigration status was less pronounced in immigrants from the Caribbean (HR 0.95; 0.91-1.00), Latin America (HR 0.85;0.82-0.91) and Africa (HR 0.80; 0.74-0.85) than in those from other world regions.

Conclusions — Immigrants have a lower rate of stroke or TIA than long-term residents with variation by age, stroke type and country of origin. This knowledge may be useful for developing targeted primary stroke prevention strategies.