Clima Laboral

The most consistent epidemiological finding pertaining to mental ill health and migration is the excess risk of psychotic disorders in migrants and their descendants. This finding is long-established (Ødegaard, 1932), and well-replicated (Bourque et al., 2011; Cantor-Graae & Selten, 2005). I will discuss the evidence

regarding this finding and its determinants in this Section.

There are no reasons to assume this increased incidence is an artefact of demographics (there might simply be more young men in minority groups, who have the highest risk) as incidence is still higher after adjusting for age and sex (see, for instance, Fearon et al., 2006). Furthermore, whilst it appears to be true that there are, for instance, ethnic differences in pathways to care (Morgan, Mallett, Hutchinson, & Leff, 2004) and in the probability of being physically restrained whilst accessing mental health services (NHS Digital, 2017) there is no evidence that there are systemic racist diagnostic biases (at least, not concerning Black Caribbeans in the UK (Hickling, McKenzie, Mullen, & Murray, 1999; Lewis, Croft-Jeffreys, & David, 1990)). I therefore assume that the differential incidence rates across different ethnic groups are a true reflection of differential risk.

Theoretically, there are several reasons why rates of disorder might be increased in ethnic minority groups, including (but not limited to) ethnicity itself, pre-migration circumstances, migration itself and the post-migratory social circumstances of minorities. I discuss these potential causes in the remaining Section.

1.4.1 Ethnicity

If ethnicity, per se, is a reliable risk indicator of increased psychosis, incidence of psychosis in the general population in countries of origin such as Caribbean, North African, or Sub-Saharan African countries would be expected to be approximately as high as the incidence in the population groups from those countries in their host countries in Western Europe. The falsity of this assertion is already demonstrated in Ødegaard’s seminal study of Norwegian migrants in Minnesota: rates were higher in Norwegian emigrants than they were in the general population in Norway (Ødegaard, 1932). Rates in several relevant countries of origin have been investigated, predominantly in Caribbean countries. In Trinidad (Bhugra et al., 1996), Surinam (Hanoeman, Selten, & Kahn, 2002; Selten et al., 2005) and Jamaica (Hickling, 1995) rates were between 11 and 22 per 100,000 person years, much lower than rates of psychosis in Black Caribbean populations in

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Western Europe, and, in fact, much more in line with general population rates in host countries (Kirkbride et al., 2012; Veling et al., 2006). Two of the three studies were methodologically strong, either using the same case-finding methodology as the WHO ten-country study (Bhugra et al., 1996; Jablensky et al., 1992) or relying on well-established patient registers (Hanoeman et al., 2002), while the third relied on reporting through existing service infrastructure (Hickling, 1995). There is little evidence from other countries of origin unfortunately. The search strategy employed to expand the systematic review (Chapter 2) globally identified only one further study in South-Africa (Burns & Esterhuizen, 2008), and an ongoing multinational research project (Morgan et al., 2017).

An initial explanation offered for this finding was the so-called ‘unhealthy migrant’ effect whereby those already more vulnerable to developing psychosis were more likely to migrate (Ødegaard, 1932). This is however an implausible mechanism: migrants’ health at least initially appeared to be at least as good as the general population health in host countries (see above). There was also no empirical evidence to underpin this putative cause (Selten, Cantor-Graae, Slaets, & Kahn, 2002; van der Ven et al., 2014). Selten and colleagues established that even if the entire population of Surinam would migrate to the Netherlands (trebling the denominator) and would not contribute any extra cases, the Surinamese population in the Netherlands still faced an increased incidence of schizophrenia (Selten et al., 2002). Using Swedish conscript and population registry data, Van der Ven and colleagues assessed whether known risk factors for psychosis were more common in conscripts who later migrated than in those who remained in Sweden. They showed that the only risk factor more prevalent in later emigrants was urban upbringing, and concluded their findings provided evidence against the selective migration hypothesis (van der Ven et al., 2014).

A second reason why ethnicity shouldn’t be considered a reliable risk indicator is that it appears that various broad ethnic groups are differentially affected across various host countries. An example is people of Black Caribbean descent. In England, their risk is higher than any other ethnic group, with a pooled risk of 5.6 times higher than the general population (Kirkbride et al., 2012). In the Netherlands, people of Black Caribbean origin (from Surinam and the Dutch Antilles) are at increased risk too, but their estimated risk is limited to 2-3 times that of the general population (Veling et al., 2006). In the Netherlands, Moroccan immigrants face the highest increase in risk with incidence rate ratios (IRRs) between 4 and 6 (Veling et al., 2006), whereas in France North African migrants face no significantly increased risk (IRR: 1.4; 95%

confidence interval [CI]: 0.4-5.6) (Tortelli et al., 2014), although the wide confidence interval suggests this study might be underpowered. Sub-Saharan migrants appear most at risk in France (IRR: 7.1; 95%CI: 2.3- 21.8) (Tortelli et al., 2014).

1.4.2 Exposure to pre-migratory risk factors and the act of migrating

Various studies have sought to investigate the relationship between pre-migratory circumstances, migration itself and excess psychosis risk in migrants. These studies have examined various aspects of this

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relationship, such as age at migration (Kirkbride, Hameed, Ioannidis, et al., 2017; Pedersen & Cantor- Graae, 2012; Veling, Hoek, Selten, & Susser, 2011) and refugee-status (Anderson, Cheng, Susser,

McKenzie, & Kurdyak, 2015; Hollander et al., 2016). Refugees are at increased risk of psychosis compared with the general migrant population (Anderson et al., 2015; Hollander et al., 2016), and this is thought to be due to a combination of increased exposure to pre-migratory stressors and a more traumatic migration experience (and post-migratory factors likely also play a role) (Rechel et al., 2013).

It is not clear which age at migration conveys the greatest risk. A Dutch study showed that an earlier age of migration (0-4 years) is associated with the highest risk (Veling et al., 2011), whereas a Danish study demonstrated that in immigrants from the developed world, those who migrated aged 10-14 appeared to be at a similarly high risk (Pedersen & Cantor-Graae, 2012), and findings from East Anglia indicate that those who migrated during childhood (5-12 years) carried the highest risk (Kirkbride, Hameed, Ioannidis, et al., 2017).

While there is some evidence that pre-migratory exposure to stressors and migration contribute to excess risk in psychotic disorders in migrants, it is also clear that, despite being born in the host country and thus never having experienced either of these, second- and even third-generation migrants are still at increased risk of developing psychotic disorders or having psychotic experiences (Bourque et al., 2011; Oh, Abe, Negi, & Devylder, 2015). Moreover, the association between generational status and increased psychosis risk appears to be complex: some migrant groups in some host countries experience a higher risk in the second compared to the first generation, whereas in other groups and in other host countries the risk appears to be attenuated (Bourque et al., 2011). A further study suggests that given the same age structure, the risk across generations is approximately equal within ethnic groups (Coid et al., 2008). Pre- migratory factors and migration are unable to explain these findings.

1.4.3 Post-migratory social circumstances

The authors of the most recent meta-analysis into the higher risk of psychosis in ethnic minorities argue that it is therefore likely that post-migratory factors play an important role in this excess risk (Bourque et al., 2011) and there is some evidence to support this. For instance, in the Netherlands, there are some indications that, at a population level, there is a link between increased incidence of psychosis and high self-perceived discrimination (Veling et al., 2007), although this wasn’t replicated at an individual-level (Veling, Hoek, & Mackenbach, 2008). Most of the epidemiological investigations into the role of social circumstances as a risk factor for psychosis tend to look at their role in explaining variation in incidence in the general population at a neighbourhood level (Drukker, Krabbendam, Driessen, & van Os, 2006; Kirkbride et al., 2014; Veling et al., 2015), and not specifically at how they explain excess risk in (ethnic) minorities. An exception to this neighbourhood-level focus is a case-control study (Morgan et al., 2008), where the authors showed that markers of social disadvantage were more prevalent in the Black Caribbean population, and suggested this contributed to their excess risk.

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