The incidence of psychotic disorders in the Republic of Ireland: a systematic review

Objectives: Despite a substantial epidemiological literature on the incidence of psychotic disorders in Ireland, no systematic review has previously been undertaken. Such evidence can help inform understanding of need for psychosis care. Methods: We conducted a prospectively-registered systematic review (PROSPERO: CRD42021245891) following PRISMA guidelines. We searched four databases (Medline, PsycInfo, Web of Science, Embase) for papers containing incidence data on non-organic psychotic disorders, published between 1950-2021 in the general adult population. We conducted duplicate screening, risk of bias assessments, and extracted data to a standardised template. We undertook a narrative synthesis for each major diagnostic outcome. Random effects meta-analyses were conducted for comparisons with ≥5 incidence rates. Results: Our search yielded 1,975 non-duplicate citations, of which 23 met inclusion criteria, containing incidence data ascertained between 1974 and 2016 (median study quality: 5/8; interquartile range: 4-6). Incidence of all psychotic disorders (N=4 studies) varied from 22.0 (95%CI: 17.3-28.0) in Dublin to 34.1 per 100,000 person-years (95%CI: 31.0-37.5) in Cavan and Monaghan. The pooled incidence of schizophrenia (N=6 studies, N=8 settings) was 20.0 per 100,000 person-years, though with imprecision around this estimate (95%CI: 10.6-37.5; I2: 97.6%). Higher rates of most outcomes were observed in men. There was consistent evidence of raised rates in more deprived and fragmented social environments, but no clear pattern by rural-urban status. Conclusions: Patterns of incidence of psychotic disorders in Ireland are broadly consistent with the wider literature from the Global North. These findings could help to identify populations at higher risk of developing psychotic disorder in Ireland.