title: Seasonal variation in the incidence of aneurysmal subarachnoid hemorrhage associated with age and gender: 20-year results from the Yamaguchi cerebral aneurysm registry.
abstract: BACKGROUND
  This study was a cerebral aneurysm registry study conducted in a region with few climatic differences. Based on data collected for over 20 years, seasonal variations and characteristics of subarachnoid hemorrhage (SAH) due to ruptured aneurysms were analyzed.
  
  
  METHODS
  This study included 5,007 patients in the Yamaguchi Prefecture with aneurysmal SAH between 1986 and 2005. Incidence rates by month, sex, age, severity, and aneurysm site were analyzed.
  
  
  RESULTS
  In women, seasonal variation was observed, in particular among those aged ≥50 years. Among those aged 50-69 years, the highest incidence was in October, and the nadir was in June (peak-to-trough ratio = 1.72). At age ≥70 years, this was slightly different, with the highest incidence in December and the nadir in July (peak-to-trough ratio = 1.48). However, there was no seasonal variation in men overall; it was limited to elderly men at age ≥70 years, with the highest incidence in January and the nadir in July (peak-to-trough ratio = 2.9). Aneurysm site and severity showed no relationship with seasonal variation.
  
  
  CONCLUSIONS
  The present study shows seasonal variations in the onset of SAH. Seasonal variations in SAH differed depending on age and sex.
authors.affiliation: Department of Neurosurgery, Yamaguchi University School of Medicine, Yamaguchi 755-8505, Japan. hishi@yamaguchi-u.ac.jp
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Ishihara
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kunitsugu
authors.forename: Sadahiro
authors.initials: S
authors.lastname: Nomura
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Koizumi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yoneda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Shirao
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Oka
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Morihiro
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yoshino
authors.forename: Michiyasu
authors.initials: M
authors.lastname: Suzuki
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D017542:Aneurysm, Ruptured / Q000453:epidemiology*; D002980:Climate; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012042:Registries; D012307:Risk Factors; D012621:Seasons; D012737:Sex Factors; D013345:Subarachnoid Hemorrhage / Q000453:epidemiology*