Increased rates of psychosis among immigrants to Sweden: is migration a risk factor for psychosis?

Background. Previous studies have shown high rates of psychosis among Afro-Caribbean immigrants to the UK and immigrants to the Netherlands. Rates of schizophrenia-like psychoses (SLP), i.e. schizophrenia or other non-affective psychosis, among the native-born and immigrant populations were assessed in Malmo, the city in Sweden with the highest proportion of immigrants. Methods. All adult patients admitted for in-patient psychiatric treatment in Malmo during the course of a 1-year period (N = 1162) were studied with regard to ethnicity and SLP diagnosis. A smaller sample consisting only of first-onset SLP cases (regardless of in- or out-patient status) was also studied (N = 56). Risks for admission and first-onset were calculated on the basis of current background population figures for Malmo. Results. Compared with those who were native-born, immigrants had increased risk for admission for SLP, with a similar tendency for increased risk for first-onset of SLP. Relative risk for SLP admission was most markedly increased in immigrants from East-Africa. Background factors specifically associated with migration (e.g. extreme duress) did not appear to contribute strongly to SLP in immigrants. Conclusion. While the current results add to the growing body of evidence showing increased risk for psychosis in immigrants, vulnerability to psychosis may have: been determined by factors other than the migration process.