Seasonality of Mania: a Tasmanian study

Objective: The aim of the study was to examine the seasonal incidence of mania in a new Southern Hemisphere location. Method: Using the Tasmanian psychiatric database, monthly admission rates were compared with expected admission rates for mania for the period 1983 to 1989. ICD-9 criteria for mania single episode (296.0) and mania recurrent episodes (296.1) were used, excluding individuals with a bipolar disorder (296.4 to 296.89). Results: One thousand three hundred and twenty-eight persons were admitted during this period. There was a significant monthly variation with admissions occurring most commonly in the summer, but this was not consistent during the seven year period. Conclusions: There was a statistically significant but inconstant summer excess. The inconstancy of the finding suggests that the phenomenon is not a simple consequence of light duration, and closer examination of these inconsistencies may lead to further elucidation of the phenomenon.