Stroke case fatality shows seasonal variation regardless of risk factor status in a Japanese population: 15-year results from the Takashima Stroke Registry.

BACKGROUND: Seasonal variation in fatality caused by stroke was examined using 15 years of data from a stroke registry of a Japanese population.

METHODS: Data were obtained from the Takashima Stroke Registry, which covers approximately 55,000 residents in central Japan. There were 1,650 registered cases of first-ever stroke between 1988 and 2002. 7- and 28-day fatality rates and 95% confidence intervals were calculated for winter, spring, summer and autumn. After adjusting for gender, age at onset and risk factors, the hazard ratios for fatal strokes in winter, spring and autumn were calculated, with summer serving as the reference.

RESULTS: For cerebral infarction, the highest 7- and 28-day fatality rates occurred during spring and winter, where they were more than double the rate during summer. The severest strokes were also more likely to occur during winter and spring. A high spring and winter hazard ratio for 28-day mortality was present in both lacunar and nonlacunar subtypes, in both genders and in subjects < 65 and > or = 65 years of age. No apparent seasonal pattern was observed for cerebral hemorrhage or subarachnoid hemorrhage. The spring and winter excess fatality persisted even after adjusting for age, gender and risk factors.

CONCLUSION: Patients who suffer an ischemic stroke during winter or spring have a poorer prognosis. Further investigation is needed to determine the factors that explain this excess risk.