The incidence of psychotic disorders has increased in more recent birth cohorts

1. The incidence of psychotic disorders in Ontario has increased in more recent birth cohorts, and the age of diagnosis has decreased.

Evidence Rating Level: 2 (Good)

The incidence trends of psychotic disorders over time in high-income countries have varied across studies and may not capture birth cohort differences that are affected by varying exposures to risk factors. This study thus examined whether the incidence of psychotic disorders has changed across birth cohorts. This retrospective, population-based cohort study using data from 7 health administrative databases in Ontario, Canada, between January 1, 1992, and December 31, 2023, included people aged 14-50 years born between 1960 and 2009. People born between 1960 and 2009 were categorized into 5-year birth cohorts. The primary outcome was diagnosis or care for a nonaffective psychotic disorder, including schizophrenia and schizoaffective disorder SSD, psychosis not otherwise specified (NOS), or both. Out of the 12,231,314 people included in the study, 152,587 (0.9%) were diagnosed with a psychotic disorder (female [%] = 58,860 [38.6]) during the study period. Between 1997 and 2023, the annual incidence of psychotic disorders increased by 60% (62.5 to 99.7 per 100,000 people) among people aged 14 to 20 years. Among those aged 21 to 50 years, incidence rates declined over time, with reductions ranging from of 32.6% to 62.0% across age groups. Compared with those born in 1975 to 1979, the incidence of schizophrenia among those born in 2000 to 2004 was 70% higher (incidence rate ratio [IRR] 1.70, 95% CI interval, 1.63 to 1.78), with increases in psychosis NOS (IRR 2.89, 95% CI 2.73 to 3.06) across birth cohorts being greater than those in SSD (IRR 1.32, 95% CI 1.25 to 1.40). Compared with those born in 1975 to 1979, the percentage of people diagnosed with a psychotic disorder at age 20 years was 104% higher (0.55% vs 0.27%) for those born in 2000 to 2004, and 37.5% higher (1.32% vs 0.96%) at age 30 years for those born in 1990 to 1994. Overall, this study found that the incidence of psychotic disorders in Ontario has increased in more recent birth cohorts and that the age of diagnosis has decreased. Although these findings may reflect improved access to assessment, future research should investigate potential contributors to these trends to inform psychosis intervention services.

Click here to read this study in CMAJ

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