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.