Abstract
Objective
There is conflicting evidence in recent literature about whether the incidence of schizophrenia is increasing or decreasing. A role for prenatal and early childhood viral infections in the aetiology of schizophrenia has also been debated. We examined the incidence of schizophrenia and the catatonic subtype of schizophrenia over a 30‐year period in Finland. We also investigated whether the incidence rate of the catatonic subtype of schizophrenia was linked to changes in exposure to viral infection (polio and measles) during the prenatal or infant period.
Methods
Persons with schizophrenia were identified from the Hospital Discharge Register. Cumulative incidence of schizophrenia from 1956 to 1989 in 4 age groups was calculated with follow‐up from 1972 to 2014. Annual rates of polio and measles were derived from nationwide registers. The association between log‐transformed polio and measles incidence and incidence of schizophrenia, and specifically catatonic schizophrenia, were analysed using linear models.
Results
Cumulative incidence of schizophrenia among individuals born 1956–1989 decreased by 23% (from 13 to 10 cases per 1000 live births). The decline was the most prominent in those with onset of schizophrenia diagnosed 16–25 years of age (−41%). The incidence of catatonic schizophrenia declined by 90% over three decades, and there was a significant association between annual polio incidence during the birth year and incidence of catatonic schizophrenia.
Conclusions
The results indicate that the incidence of schizophrenia in Finland has declined for individuals born between 1956 and 1989, and that the decline of catatonic schizophrenia may be partially attributable to eradication of polio.