Association of Environment With the Risk of Developing Psychotic Disorders in Rural Populations

Abstract

Social determinants are important risk factors for the development of first-episode psychosis (FEP); their effects in rural areas are largely unknown. To investigate neighborhood-level factors associated with FEP in a large, predominantly rural population-based cohort. This study extracted data on referrals for treatment of potential FEP at 6 Early-Intervention Psychosis services from the Social Epidemiology of Psychoses in East Anglia naturalistic cohort study data set, which covered a population of more than 2 million people in a rural area in the East of England for a period of 3.5 years. All individuals aged 16 to 35 years who presented to Early-Intervention Psychosis services and met diagnostic criteria for first episodes of nonaffective psychoses and affective psychoses (International Statistical Classification of Diseases and Related Health Problems, Tenth Revision diagnostic codes F20-33) were included (n = 631). Persons whose disorders had an organic basis (diagnostic codes F06.X) and those meeting the criteria for substance-induced psychosis (diagnostic codes F1X.5) were excluded. We derived 4 neighborhood-level exposures from a routine population data set using exploratory factor analysis (racial/ethnic diversity, deprivation, urbanicity, and social isolation) and investigated intragroup racial/ethnic density and fragmentation. Multilevel Poisson regression was performed to determine associations between incidence rates and neighborhood-level factors, after adjustment for individual factors. Results were reported as incidence rate ratios (IRRs). The study included 631 participants who met criteria for FEP and whose median age at first contact was 23.8 years (interquartile range, 19.6-27.6 years); 416 of 631 (65.9%) were male. Crude incidence of FEP was calculated as 31.2 per 100 000 person-years (95% CI, 28.9-33.7). Incidence varied significantly between neighborhoods after adjustment for age, sex, race/ethnicity, and socioeconomic status. For nonaffective psychoses, incidence was higher in neighborhoods that were more economically deprived (IRR, 1.13; 95% CI, 1.06-1.20) and socially isolated (IRR, 1.11; 95% CI, 1.04-1.19). It was lower in more racially/ethnically diverse neighborhoods (IRR, 0.94; 95% CI, 0.87-1.00). Higher intragroup racial/ethnic density (IRR, 0.97; 95% CI, 0.94-1.00) and lower intragroup racial/ethnic fragmentation (IRR, 0.98; 95% CI, 0.96-1.00) were associated with a reduced risk of affective psychosis. Spatial variation in the incidence of nonaffective and affective psychotic disorders exists in rural areas. This suggests that the social environment contributes to psychosis risk across the rural-urban gradient.