title: The incidence of schizophrenia and schizophrenia spectrum disorders in Denmark in the period 2000-2012. A register-based study.
abstract: We aimed to examine changes over time in the incidence of broad and narrow schizophrenia spectrum disorders in Denmark from 2000 to 2012.
  
  
  
  Patients were classified as incident schizophrenia if registered with a first time in- or outpatient contact with relevant diagnostic codes in the Danish Psychiatric Central Register between 2000 and 2012. Their history of contacts was traced back to 1969. Broad schizophrenia included schizophrenia, schizotypal disorder, persistent delusional disorder, acute and transient psychotic disorders, schizoaffective disorders, and other nonorganic and unspecified psychotic disorders, (ICD 10 codes F20-F29). Narrow schizophrenia was defined with the ICD 10 codes F20.0-F20.9. Incidence rates (IR) and incidence rate ratios (IRR) were calculated using Poisson regression.
  
  
  
  The IRR for broad schizophrenia increased by 1.43 (CI 95% 1.34-1.52) for females and 1.26 (CI 95% 1.20-1.33) for males. IRR for narrow schizophrenia increased by 1.36 (CI 95% 1.24-1.48) for females and 1.20 (CI 95% 1.11-1.29) for males. There was a significantly increased incidence in patients up to 32years of age. This was mainly explained by a significant 2-3 fold increase in outpatient incidence. We found a significant decrease in IRR for patients with broad and narrow schizophrenia aged 33 or older for both in- and outpatients.
  
  
  
  The increased incidence of schizophrenia could partly be explained by better implementation of the diagnostic criteria for schizophrenia in child and adolescent psychiatry and improved access to early intervention services, but a true increase in incidence of schizophrenia cannot be excluded. The decrease of incidence in the older age group could indicate that the national Danish early intervention strategy was successful.
authors.affiliation: Mental Health Center Copenhagen, Mental Health Services in the Capital Region of Denmark, Denmark; Institute for Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
authors.forename: Johanne Olivia Grønne
authors.initials: JOG
authors.lastname: Kühl
authors.affiliation: National Centre for Register-based Research, Aarhus University, Denmark; iPSYCH The Lundbeck Foundation Initiative for Integrated Psychiatric Research, Denmark.
authors.forename: Thomas Munk
authors.initials: TM
authors.lastname: Laursen
authors.affiliation: Mental Health Center Copenhagen, Mental Health Services in the Capital Region of Denmark, Denmark; Institute for Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark; Child and Adolescent Mental Health Services, Capital Region of Denmark, Denmark; iPSYCH The Lundbeck Foundation Initiative for Integrated Psychiatric Research, Denmark.
authors.forename: Anne
authors.initials: A
authors.lastname: Thorup
authors.affiliation: Mental Health Center Copenhagen, Mental Health Services in the Capital Region of Denmark, Denmark; Institute for Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark; iPSYCH The Lundbeck Foundation Initiative for Integrated Psychiatric Research, Denmark. Electronic address: mn@dadlnet.dk.
authors.forename: Merete
authors.initials: M
authors.lastname: Nordentoft
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000553:Ambulatory Care; D002648:Child; D002675:Child, Preschool; D003702:Delusions / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D008297:Male; D011446:Prospective Studies; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D012042:Registries; D012044:Regression Analysis; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D012569:Schizotypal Personality Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D012737:Sex Factors; D055815:Young Adult
keywords: Early detection; Epidemiology; First episode psychosis; Incidence; Schizophrenia