A recent article which I reviewed found evidence for an increasing incidence of schizophrenia in Canada. The researcher speculated that Canada’s high rate of immigration may contribute to this finding. Studies from other industrialized countries have found that immigrants, both in the first and second generation, have an elevated risk of developing schizophrenia, but evidence of this in Canada is lacking. A group from the Centre for Addictions and Mental Health in Toronto estimated the incidence of schizophrenia and schizoaffective disorder in Ontario, the most populous and immigrant-rich province of Canada, by examining hospital and billing records with the records maintained by Canadian immigration authorities.
The identified cohort was all Ontario residents who were age 14 to 40 years at the beginning of the 10-year period from 1999-2008. Because of the universal health-care system, all people who come to medical attention have their diagnosis recorded in a provincial data set. All those listed as an immigrants by the federal ministry of citizenship were classified as such whereas all those not listed were classified as non-immigrants. The investigators also noted which immigrants were admitted under refugee status, an indication of a more vulnerable and likely trauma-exposed group.
The rate of new-onset psychosis in the general population was 55.6 (95% CI 54.9–56.4) per 100 000 person-years and 51.7 (95% CI 49.2–54.4) per 100 000 person-years in first-generation immigrants; these rates are not significantly different. Among the immigrants classified as refugees, the rate was higher: 72.8 (95% CI 67.1– 78.9) per 100 000 person-years, but this is not significantly different from the other rates. Closer examination found that immigrants of various origins had differing rates; those from the Caribbean and Bermuda had significantly higher risk whereas those from northern and southern Europe and east Asia had significantly lower risk than the general population. Among refugees, those from east Africa and south Asia had significantly greater risk of psychosis than the general population.
The shortcomings of this kind of study are considerable, mainly the retrospective design and the reliance on administrative-level diagnostic data. Furthermore, the general population included second-generation immigrants who could not be identified by the study methods but who also probably have a higher risk of psychosis. Moreover, the researchers mention that refugees often have other mental illnesses such as posttraumatic stress disorder which may be misdiagnosed as psychosis. Despite these sources of bias, the findings support an emerging theoretical framework in which those immigrants most subject to discrimination, often because of their race, may be most vulnerable to onset of psychosis. Socioeconomic factors and trauma also likely play a role. Early intervention programs may increase their effectiveness by taking this into consideration. The findings also underline the significance of the federal role in health-care funding for refugees, a highly vulnerable population.
Anderson KK, Cheng J, Susser E, McKenzie KJ, Kurdyak P. Incidence of psychotic disorders among first-generation immigrants and refugees in Ontario. CMAJ. 2015;17:e279-e286. Article