Immigration, region of origin, and the epidemiology of venous thromboembolism: A population‐based study

BACKGROUND: Venous thromboembolism (VTE) epidemiology has been mainly studied in populations largely of European ancestry. OBJECTIVES: To assess the epidemiology of VTE in immigrants to Ontario, Canada. PATIENTS/METHODS: We conducted a population‐based retrospective cohort study using linked health‐care and administrative databases. We included 1 195 791 immigrants to Ontario and 1 195 791 nonimmigrants, matched on age, sex, and place of residence. The main exposure was ethnicity according to world region of origin, using a previously validated algorithm. The main outcome was incident onset of VTE during the period of observation. Risk ratios (RR) were calculated using Poisson regression models. RESULTS: The incidence rate (IR) of VTE was lower among immigrants (0.87 per 1000 PY; 95% confidence interval [CI] 0.85‐0.89) than nonimmigrants (1.59 per 1000 PY; 95% CI 1.56‐1.61). Age‐ and sex‐standardized IR were lower among East and South Asian immigrants. Compared to immigrants for predominantly White regions, age‐ and sex‐specific RRs were consistently lower for East Asian (0.18‐0.30) and South Asian (0.29‐0.75) immigrants. In contrast, the RRs of VTE among Black (0.38‐1.50), Latin American (0.29‐1.25), Arab/Middle Eastern (0.44‐1.08) and West Asian (0.31‐1.16) immigrants were not significantly different from White immigrants. CONCLUSIONS: In Ontario, the incidence of VTE is lower among immigrants compared to nonimmigrants. East and South Asian immigrants have a lower risk of VTE compared to White immigrants.