Trends in the incidence of subarachnoid hemorrhage in Akita Prefecture, Japan

Abstract

Object The incidence of subarachnoid hemorrhage (SAH) in Japan has been reported to be among the highest in the world. The aim of this study was to analyze the incidence of SAH and its trends in Akita Prefecture, Japan. Methods The incidence rate of SAH between January 1, 1989, and December 31, 1998, was investigated using the prospective Akita Stroke Register. Computed tomography scans were obtained in all suspected cases of SAH. During the study period, 3257 patients with their first SAH were registered. The crude annual incidence rates of SAH in men, women, and both sexes were 20, 33, and 27 per 100,000 population per year, respectively. Age-standardized incidence rates remained stable. Crude incidence rates in women increased. In men the incidence reached a plateau after 55 years of age; in women it peaked in the eighth decade of life. The 28-day case fatality rate was 26.7%, without significant changes. Two diurnal peaks were observed: one at 7 a.m. and another at 5 p.m. The incidence was lowest in summer and highest in spring, in both sexes. Conclusions The incidence of SAH in patients in Akita Prefecture is similar to that reported in other Japanese studies. The age-standardized incidence rates are stable. The increasing crude incidence in women is probably attributable to the aging of the Japanese population.