M130. COMPARISON OF CUMULATIVE INCIDENCE OF HOSPITAL TREATED PSYCHOSIS IN FIVE FINNISH BIRTH COHORTS
Authors: Kerkelä Martta , Gissler Mika , Gyllenberg David , Sourander Andre , Veijola Juha 
Published: May 2020

Abstract

Background
Finnish mental health policy has aimed to reduce psychiatric inpatient beds and the average duration of psychiatric inpatient treatment period has been reduced noticeably since 1980s. At the same time, the aim has been to increase outpatient services for people with schizophrenia and other psychotic disorders. Along with this policy, there is some evidence that increasing number of people with psychosis have never been admitted to hospital.
The purpose of this study was to harmonize health care data in five large Finnish birth cohorts and evaluate evidence on whether the cumulative incidence of adolescent and adulthood hospitalization due to schizophrenia and other psychotic disorders has changed over the decades.

Methods
We used data from five different Finnish birth cohorts: Northern Finland Birth Cohort 1966 (NFBC 1966), 1987 Finnish Birth Cohort (FBC 1987), Finnish 1981 Birth Cohort Study (FBCS 1981), Northern Finland Birth Cohort 1986 (NFBC 1968) and 1997 Finnish Birth Cohorts (FBC 1997).
NFBC 1966 includes the people born in the two northern most provinces of Finland with the expected date in the year 1966, comprising of 12,231 children and the NFBC 1986 between July 1st, 1985 and June 30th, 1986 including 9,479 children. FBCS 1981 consist of a sample including 10% of the Finnish children born in 1981. The sample is based on the school sampling, comprising of 5,417 children. FBC studies follows all children survived perinatal period born in Finland in 1987 and in 1997. FBC 1987 comprises of 59,476 children and FBC 1997 of 58,802 children.
The main outcome in this study was hospitalization due to schizophrenia and other psychotic disorders. The data of mental disorders were obtained from the Care Register for Health Care (CRHC). Data covers the years from 1969 to 2017. The CRHC data was harmonized in each cohort using the same program. The harmonization included personal identification number and dates (entry date, date of discharge) revisions. The diagnoses were confirmed to be on the right format.
Final dataset included total N = 145,405 subjects. The follow-up for the study subjects was from age 0 to 18 years in all five birth cohorts and from age 0 to 28 years in all other cohorts except FBC 1997.
Cumulative incidence of hospital treated schizophrenia and other psychotic disorders in each cohort was calculated. Test of equal proportions was used to calculate the Pearson’s chi-squared statistic. The linear association was also tested using chi-squared test for trend in proportions.

Results
At ages of 0 to 28 years the cumulative incidences of hospital treated psychosis were in NFBC 1966 1.0% (N=124), FBCS 1981 1.5% (N=81), NFBC 1986 1.2% (N=109) and FBC 1987 1.6% (N=947) (χ²: 30.6, p&lt;.001; χ²trend: 23.5, p&lt;.001). Respective numbers at age of 0 to 18 years were in NFBC 1966 0.1% (N=14), FBCS 1981 0.3% (N=15), NFBC 1986 0.3% (N=33), FBC 1987 0.4% (N=256) and FBC 1997 0.3% (N=195) (χ²: 31.6, p&lt;.001; χ²trend: 9.9, 0.001).
Hospital treated schizophrenia between ages of 0 to 18 years was too rare to analyze (NFBC 1966 N=5, FBCS 1981 N=4, NFBC 1986 N=4, FBC 1987 N=41 and FBC 1997 N=15). At ages of 0 to 29 years the cumulative incidences were NFBC 1966 0.4% (N=59), FBCS 1981 0.6% (N=34), NFBC 1986 0.3% (N=27) and FBC 1987 0.5% (N=297) (χ²: 10.5 p=0.015; χ²trend: 0.01, p = 0.912).

Discussion
The main finding of the study was that the cumulative incidence of first-admission inpatient treated psychosis has increased over the decades in Finland. This is somewhat opposite to the Finnish mental health policy plan aiming to treat people with schizophrenia and other psychotic disorders mainly in outpatient services.