Heterogeneity in Incidence Rates of Schizophrenia and Other Psychotic Syndromes

CONTEXT: Convention suggests uniformity of incidence of schizophrenia and other psychoses; variation would have implications for their causes and biological characteristics. OBJECTIVE: To investigate variability in the incidence of psychotic syndromes in terms of place, ethnicity, age, and sex. DESIGN: Three-center, prospective, comprehensive survey of clinically relevant first-onset psychotic syndromes over a 2-year period (1997-1999). Census data provided the denominator. SETTING: Southeast London, Nottingham, and Bristol, England. PARTICIPANTS: One million six hundred thousand person-years yielded 568 subjects aged 16 to 64 years with clinically relevant psychotic syndromes. MAIN OUTCOME MEASURES: The World Health Organization Psychosis Screen and the Schedules for Clinical Assessment in Neuropsychiatry to classify, blind to ethnicity, all DSM-IV psychotic syndromes and the subclasses of schizophrenia, other nonaffective disorders, affective disorders, and substance-induced psychosis. RESULTS: All syndromes showed a characteristic age distribution. Schizophrenia was significantly more common in men (incidence rate ratio IRR, 2.3 95% confidence interval (CI), 1.7-3.1); affective disorders occurred equally in men and women (IRR, 1.0 95% CI, 0.7-1.3). All psychoses were more common in the black and minority ethnic group (crude IRR, 3.6 95% CI, 3.0-4.2). Differences in age, sex, and study center accounted for approximately a quarter of this effect (adjusted IRR, 2.9 95% CI, 2.4-3.5) in each psychosis outcome. The age-sex standardized incidence rate for all psychoses was higher in Southeast London (IRR, 49.4 95% CI, 43.6-55.3) than Nottingham (IRR, 23.9 95% CI, 20.6-27.2) or Bristol (IRR, 20.4 95% CI, 15.1-25.7). Rates of all outcomes except affective disorders remained significantly higher in Southeast London when the model was expanded to control for ethnicity. CONCLUSIONS: There is significant and independent variation of incidence of schizophrenia and other psychoses in terms of sex, age, ethnicity, and place. This confirms that environmental effects at the individual, and perhaps neighborhood level, may interact together and with genetic factors in the etiology of psychosis.