This is a novel study and it contradicts most clinical knoweledge. There are some problems, which the authors correctly note, but the quickest summary comes from the editorial on the paper which is in prepublication form at JAMA Psychiatry. From my point of view, the main issue is that this paper shows marked variations, which are significant, between places.
But the first thing to note is that you can become psychotic at any age, and women are more likely to develop such an event in later life than men: when you have almost 3000 people with breakthrough psychosis this is a little more obvious.
Jongsma et al publish an extraordinary study designed to compare incidence rates of all psychotic disorders in 17 settings in 6 countries. The study included 2774 people with psychotic disorders detected at the time that the patients presented for treatment at mental health services. This study differs in important ways from the Ten Country Study.1 The settings are less diverse, with all but 1 located in western Europe and more than half located in either Spain (n?=?6) or Italy (n?=?3). This reduces sociocultural contrasts but made the study more tractable for examining measured dimensions of social context that might explain variation across settings. Recent developments in theory and empirical research facilitated the choice of contextual measures.5 Moreover, the study is an integral part of a broader scientific initiative focused on gene-environment interactions, the European Network of National Schizophrenia Networks Studying Gene-Environment Interactions. The study also reports on individual characteristics (age, sex, and racial/ethnic minority status), but the comparisons across settings in different countries were the most novel contribution.
The initial results are intriguing and somewhat surprising. Jongsma et al4 report a striking 10-fold variation across study settings, from 6.3 to 61.4 cases per 100?000 person-years in the crude incidence of all psychotic disorders for people aged 18 to 64 years. This was reduced to approximately 8-fold variation after accounting for age, sex, and (at least crudely) racial/ethnic minority status. Results were not entirely consistent at the setting level across 3 interrelated measures of social context. A strong and important result was that some of the variation was explained by the association of a higher proportion of owner-occupied homes, a proxy for social stability and cohesion, with lower incidence of psychosis. In unadjusted analyses, a higher proportion of single-person households, a proxy for social fragmentation, was associated with higher psychosis incidence, but this characteristic did not have a detectable effect on incidence after adjustment for home ownership. Additional unadjusted analyses showed that higher unemployment, a proxy for social deprivation, was unexpectedly associated with lower incidence of psychotic disorders, but this also had no detectable effect after adjustment for home ownership.
Secondly, let us look at the places. The highest rates are in London, Amsterdam and Paris: the lower rates are in Spain, Brazil and rural/provincial centres. What is unspoken is that London, Amsterdam and Paris are far more diverse, and that the immigrant risk of psychosis is known.
There have to be some caveats with this approach. We may be missing cases: in my experience when people are mad, they are bought to the attention of acute wards, willing or unwilling, immigrant or not, high social status or not. The move in the English speaking places (and in parallel Holland) may be a factor, but Southern Europe and Brazil have fairly well developed psychosis services. And the variation is marked.
Detection of patients who never present to services is an issue for all epidemiologic studies, and our rate estimates should be interpreted as the treated incidence. Although our overarching case ascertainment method was similar across all settings, some adaptation to local health care systems was necessary. For example, primary care in each catchment area may have referred different proportions of patients with FEP to secondary mental health care services, but referral guidelines were very similar across national settings; these guidelines all urge prompt referral of anyone with FEP. That said, we did not assess whether referral practices were consistent within and between catchment areas. Difference in the average timing of referral may have affected the case mix within the FEP category, but not the overall number of referrals; each center was in a steady state.
Differences in the organization of secondary mental health care services across localities may also have influenced detection of patients. In England and the Netherlands, for example, the widespread commissioning of early intervention in psychosis services may have led to improved detection of new cases of FEP. The leakage study in Brazil revealed a substantial number of new cases at this site (279 [49%]), while similar approaches in 2 French sites (Paris and Val-de-Marne) identified far fewer missed cases (7 [6%] in Paris and 28 [13%] in Val-de-Marne).30 Comprehensive, regular contact with mental health services should have helped minimize underascertainment, although some patients, including those treated privately, may have been missed; in general, we believe these biases are unlikely to account for the 8-fold variation between catchment areas.
Which leaves us, particularly as owner occupancy correlates with lower rates of psychosis, with a question: is the increasing rate of madness (which we are seeing) a consequence of diversity, or not? For London is no longer like England, and the Parisian Banleaux are no longer part of France.