IS THE DECLINE IN DIAGNOSES OF SCHIZOPHRENIA CAUSED BY THE DISAPPEARANCE OF A SEASONAL ETIOLOGIC AGENT - AN EPIDEMIOLOGIC-STUDY IN ENGLAND AND WALES

Background. Studies from several countries have shown a decline, in th e last few decades, of the number of admissions with a diagnosis of sc hizophrenia. This could be due to a fall in the incidence of schizophr enia, 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 aetiologi cal agent. Methods. The hypothesis was tested by analysing the dates o f birth of the patients discharged with a diagnosis of schizophrenia f rom NHS hospitals in England and Wales and would be confirmed by an ap propriate change in the seasonality of the births over time. Results. Evidence of seasonality has been observed in the schizophrenic births, but with no significant change over time. Conclusions. The fall in fi rst admissions with a diagnosis of schizophrenia does not seem to be d ue to a change in the prevalence of a seasonal aetiological factor. Th erefore, either there has been a reduction in incidence due to a chang e in a non-seasonal agent, or the incidence of schizophrenia is not ch anging and the fall in first admissions is due to confounding factors.