Background: Findings from various temperate regions have quite consistently shown a spring/summer peak for the occurrence of manic episodes, but inconsistencies can still be found in results from tropical regions. The present study was designed to investigate the seasonal distribution of mania and its correlations to climatic variables, in a large sample of patients visiting the emergency psychiatric room.
Methods: A hospital registry of 5172 emergency psychiatric visits for mania, 2000-2007, at a public psychiatric hospital at Belo Horizonte, Brazil (latitude 19 degrees 55' S), was analyzed. Seasonality was assessed with Cosinor Analysis. Correlations of the rate of admissions for mania to climatic variables were performed, including lagged and differenced data.
Results: A minor, but significant seasonal pattern was evidenced, with a late winter/spring peak and the nadir in February (late summer). The regression model including secular and seasonal components explained 44.4% of the variance of visits for mania. The rate of emergency visits for mania was negatively correlated to relative humidity and rainfall. Altogether, climatic variables explained 8.1% of the variance in the rate of emergency visits for mania.
Limitations: Using hospital registry data may have led to misclassification of diagnosis. The ecologic design does not account for seasonal evolution of individual cases.
Conclusion: Emergency psychiatric visits for mania were more frequent in late winter/spring, corresponding to the drier seasons of Belo Horizonte. Seasonality of mania in the tropics was corroborated by these results.