Generational Patterns of Asthma Incidence among Immigrants to Canada over Two Decades. A Population-based Cohort Study

Although asthma has been historically common in Canada, with a reported prevalence ranging between 13% and 21% (1–3), there has been a steady reduction in new asthma cases over the last 20 years (4). This reduction in asthma incidence has overlapped with a period of increased immigration from Asian countries, where endemic asthma rates are much lower (5). In the last decade, 50% of immigrants arriving to Ontario, Canada’s most populous province, were from South Asia (primarily from India, Pakistan, or Sri Lanka) and East Asia (primarily from China and Hong Kong) (6). The influence of immigration of individuals from world regions with low endemic asthma rates on overall asthma rates in Ontario has not been fully studied.

Previous measurements of asthma rates among immigrants from different parts of Asia have shown an increased risk of asthma proportional with the duration of living in Canada (2, 5). These studies also demonstrated higher rates of asthma among Canadian-born children of immigrants, relative to their parents (5, 7). Whether these findings translate to individuals immigrating from non-Asiatic regions of the world is not known.

In this study, we used population-based health administrative data to determine the incidence of asthma in immigrants to Canada and their children. Incidence of asthma was compared between immigrants from different regions of the world and long-term Ontario residents and their children, with the aim of providing further insight into the influence of environmental exposures on the development of asthma. We additionally explored the contribution of immigration to trends in overall asthma incidence in Ontario.