Is the decline in diagnoses of schizophrenia caused by the disappearance of a seasonal aetiological agent? An epidemiological study in England and Wales.

Abstract

Studies from several countries have shown a decline, in the last few decades, of the number of admissions with a diagnosis of schizophrenia. This could be due to a fall in the incidence of schizophrenia, but it also could be due to confounding factors. The hypothesis tested in the study is that the incidence of schizophrenia is actually falling because of a decrease in the presence of a seasonal aetiological agent. The hypothesis was tested by analysing the dates of birth of the patients discharged with a diagnosis of schizophrenia from NHS hospitals in England and Wales and would be confirmed by an appropriate change in the seasonality of the births over time. Evidence of seasonality has been observed in the schizophrenic births, but with no significant change over time. The fall in first admissions with a diagnosis of schizophrenia does not seem to be due to a change in the prevalence of a seasonal aetiological factor. Therefore, either there has been a reduction in incidence due to a change in a non-seasonal agent, or the incidence of schizophrenia is not changing and the fall in first admissions is due to confounding factors.