Seasonal variation of stroke incidence in Japan for 35631 stroke patients in the Japanese Standard Stroke Registry, 1998-2007.

BACKGROUND

Seasonal variation of stroke incidence has been reported in many countries. The present study was designed to elucidate seasonal and monthly variations in the incidence of subtypes of acute ischemic stroke and hypertensive hemorrhagic stroke using the Japanese Standard Stroke Registry Study (JSSRS) database, which is currently the world's largest hospital-based stroke database, accumulating records from 163 Japanese institutions.

METHODS

Among 47,782 patients with acute stroke registered with JSSRS between 1998 and 2007, we selected 35,631 for analysis (patients with ischemic or hemorrhagic stroke of unknown etiology were excluded). A simple moving average was used to examine monthly variation of stroke incidence. We also examined seasonal variation of ischemic stroke subtypes.

RESULTS AND CONCLUSIONS

Monthly variation in incidence of all ischemic stroke was significant (P < .001). Noncardioembolic ischemic stroke was more frequent in summer than in winter (P < .001). Lacunar stroke showed higher incidence in summer than in winter (P < .001), although the increase did not reach significance for atherothrombotic stroke (P = .057). In contrast, cardioembolic stroke (P < .001) and hemorrhagic stroke (P < .001) occurred more frequently in winter than in summer. Hemorrhagic stroke showed a regional difference of incidence between northern and southern Japan. There is a temporal variation of stroke incidence in Japan, with different patterns of variation depending on stroke subtype. These findings may help in developing strategies for preventing stroke.