Seasonal and Monthly Variation in Stroke and its Subtypes–10 Year Hospital-Based Study

BACKGROUND AND OBJECTIVES: There is no evidence of long-term studies of seasonal variations in stroke in Iran. Hence, the aim of this study was to determine the seasonal and monthly variation of 28-day mortality in Isfahan, Iran. METHODS: From 2003 to 2013, In a Hospital-based retrospective study which was conducted by Isfahan Cardiovascular Research Center(ICRC), 24186 cases with first-ever stroke were recruited. Multinomial logistic regression was used to calculate odds ratios (OR) with 95% confidence intervals (CI) for seasonal and monthly 28-day mortality for stroke in general and three subtypes of stroke including intracranial hemorrhage (ICH), ischemic (IS) and subarachnoid hemorrhage (SAH). RESULTS: In this study, unadjusted and adjusted odds ratios of seasonal 28-day mortality of stroke was highest in the winter and lowest in the summer. Although, differences were not statistically significant. For total and IS stroke, the unadjusted 28-day mortality ratio (UMR) was significant in February (1.19, 95% CI 1.00 -1.42, P= 0.04) as compared to March. Whereas after adjusted, for total stroke, 28-day mortality was significantly lowest in May (0.746, 95% CI 0.575-0.97, p=0.029), June (0.777, 95% CI 0.60-0.99, p=0.49) and July (0.771, 95% CI 0.59-0.99 p=0.049) as compared to March. The AMR between months were not significant in SAH and IS. CONCLUSION: Our findings demonstrate clear obvious monthly variation of 28-day mortality of stroke and its subtypes in Isfahan but no seasonal variations were observed.