Seasonal influences on admissions in schizophrenia and affective disorder in Ireland.

Although the seasonal patterns of admissions of affective disorder have been extensively studied, less attention has been given to the seasonal admission patterns of schizophrenia. The traditional method of aggregating the data over a study period, rather than analysing by year of admission may obscure potentially relevant fluctuations in the seasonal pattern. We examined the year-to-year variation in the admission patterns of schizophrenia and affective disorder in Ireland. Using the National Psychiatric Inpatient Reporting System (NPIRS), individuals admitted with an ICD-9/10 diagnosis of a first episode of schizophrenia or affective disorder during the 6-year period 1989-1994 were identified. Seasonal variations in their admission patterns were examined statistically and graphically. There was a significant seasonal variation in the monthly admission patterns of both schizophrenia and affective disorder. This pattern was more marked for individuals with affective disorder. However, the seasonal pattern was not constant from year to year, particularly for schizophrenia.