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IJE Advance Access originally published online on August 25, 2008
International Journal of Epidemiology 2009 38(5):1255-1264; doi:10.1093/ije/dyn168
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Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2008; all rights reserved.
The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions@oxfordjournals.org

Is the incidence of psychotic disorder in decline? Epidemiological evidence from two decades of research

J B Kirkbride1,*, T Croudace1, J Brewin2, K Donoghue3, P Mason4, C Glazebrook5, I Medley6, G Harrison7, J E Cooper5, G A Doody5 and P B Jones1

1 Department of Psychiatry, University of Cambridge, Box 189, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ, UK.
2 Nottinghamshire Healthcare NHS Trust, Duncan Macmillan House, Porchester Road, Mapperley, Nottingham, NG3 6AA, UK.
3 Duncan Macmillan House, Porchester Road, Mapperley, Nottingham, NG3 6AA, UK.
4 The Stein Centre, St Catherine's Hospital, Derby Road, Birkenhead, CH42 0LQ, UK.
5 Department of Psychiatry, University of Nottingham, Duncan Macmillan House, Porchester Road, Mapperley, Nottingham, NG3 6AA, UK.
6 The Mandala Centre, Gregory Boulevard, Nottingham NG7 6LB, UK.
7 Academic Unit of Psychiatry, University of Bristol, Cotham House, Cotham Hill, Bristol, BS6 6JL, UK.

* Corresponding author. Department of Psychiatry, University of Cambridge, Box 189, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ. E-mail: jbk25{at}cam.ac.uk


  Abstract

Background It is unclear whether the incidence of first episode psychoses is in decline. We had the opportunity to determine whether incidence had changed over a 20-year period in a single setting, and test whether this could be explained by demographic or clinical changes.

Methods The entire population at-risk aged 16–54 in Nottingham over three time periods (1978–80, 1993–95 and 1997–99) were followed up. All participants presenting with an ICD-9/10 first episode psychosis were included. The remainder of the population at-risk formed the denominator. Standardized incidence rates were calculated at each time period with possible change over time assessed via Poisson regression. We studied six outcomes: substance-induced psychoses, schizophrenia, other non-affective psychoses, manic psychoses, depressive psychoses and all psychotic disorders combined.

Results Three hundred and forty-seven participants with a first episode psychosis during 1.2 million person-years of follow-up over three time periods were identified. The incidence of non-affective or affective psychoses had not changed over time following standardization for age, sex and ethnicity. We observed a linear increase in the incidence of substance-induced psychosis, per annum, over time (incidence rate ratios: 1.15; 95% CI 1.05–1.25). This could not be explained by longitudinal changes in the age, sex and ethnic structure of the population at-risk.

Conclusions Our findings suggest psychotic disorders are not in decline, though there has been a change in the syndromal presentation of non-affective disorders, away from schizophrenia towards other non-affective psychoses. The incidence of substance-induced psychosis has increased, consistent with increases in substance toxicity over time, rather than changes in the prevalence or vulnerability to substance misuse. Increased clinical and popular awareness of substance misuse could also not be excluded.

Keywords Psychotic disorder, incidence, time, epidemiology, schizophrenia, demographic factors

Accepted 21 July 2008


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