Relationship between aneurysmal subarachnoid hemorrhage and climatic conditions in the subtropical region, Amami-Oshima, in Japan.

Epidemiological studies of the relationship between climate and the onset of aneurysmal subarachnoid hemorrhage (SAH) have been reported in the temperate and subarctic latitudes. However, the relationship between the incidence of aneurysmal SAH and the climatic variations in the subtropical region remains uncertain. Epidemiological analysis requires study of an extremely isolated area. This study analyzed the relationship between the onset of aneurysmal SAH and climatic conditions in the isolated subtropical island of Amami-Oshima in Japan. During an 11-year period from 1986 to 1996, 210 patients with a primary diagnosis of aneurysmal SAH were identified by computed tomography and angiography. The mean annual age-adjusted incidence of aneurysmal SAH was 15.5 per 100,000 population (10.4 for males and 20.6 for females). No significant seasonal variations in the incidence of aneurysmal SAH and admission clustering were observed in males (p > 0.05) or females (p > 0.05). Furthermore, temperature, atmospheric pressure, and relative humidity were not significantly correlated with the monthly incidence of aneurysmal SAH. However, the occurrence of aneurysmal SAH tended to be higher in both females and the elderly during the winter and spring seasons and not during other seasons. This study indicates that seasonal and climatic conditions do not strongly contribute to the incidence of aneurysmal SAH in subtropical regions. However, elderly people are affected more by climatic conditions than young people.