The Declining Incidence Rate of Subarachnoid Hemorrhage in Four Local Japanese Regions Is Greater in Women than in Men: Japan Incidence of Subarachnoid Hemorrhage Study

Female sex is an independent risk factor for subarachnoid hemorrhage. Additionally, the global decline in the incidence rate of subarachnoid hemorrhage is more apparent in men than in women, except in Japan. We examined sex-specific trends in the incidence rates of subarachnoid hemorrhage in four Japanese regions. An epidemiological study was conducted to identify the estimated age-adjusted incidence rate of subarachnoid hemorrhage per 100,000 person-years by sex in Aomori, Akita, Kochi, and Shimane Prefectures from 2000 to 2017, calculated by the age-adjusted mortality and case-fatality rates (assumed to be 35%). The estimated age-adjusted incidence rate of subarachnoid hemorrhage in each region decreased in both sexes between 2000 and 2017; the rates of change were significantly higher in women (43.1%) than in men (36.6%; p = 0.021). This study revealed declining trends in the estimated age-adjusted incidence rate of subarachnoid hemorrhage in four Japanese prefectures from 2000 to 2017; this was more apparent in women. The underlying etiology for the female-dominant declining trend in the estimated age-adjusted incidence rate of subarachnoid hemorrhage should be further investigated.