Seasonality of first admissions for schizophrenia in the Southern Hemisphere.

Northern Hemisphere studies of first admissions for schizophrenia have shown an excess of summer admissions (June, July and August) compared to other times of the year. The within-year fluctuations in first admissions could be related to meteorological factors that fluctuate between seasons (e.g. temperature, photoperiod) and/or social factors (e.g. holidays, religious events). If meteorological factors were primarily responsible for the fluctuation, then Southern Hemisphere studies should find excess first admissions in December, January and February. This paper presents the first season of first admission study of schizophrenia in the Southern Hemisphere. The month and year of first admission for schizophrenia (ICD 8/9) for 4487 male and 3252 female, Australian-born individuals were extracted from a Queensland mental health register. Spectral analysis showed a strong annual periodicity of first admissions for males with the peak in August (Southern Hemisphere winter) and a trough in the summer months (December to February). The pattern for females also displayed annual periodicity. These results correspond to the Northern Hemisphere reports of excess of schizophrenia first admissions in terms of the month of the year but not the season of excess. Further work is needed in order to clarify the impact of latitude and meteorological factors on the month of first admission for schizophrenia.