title: A temporal pattern in the occurrence of aneurysmal subarachnoid hemorrhage in the Province of Vojvodina, Serbia.
abstract: BACKGROUND
  Numerous studies with conflicting results have tried to prove the influence of seasonal variations or different meteorological factors on the occurrence of aneurysmal subarachnoidal hemorrhage (SAH). The aim of this study was to establish a mathematical model of a series of aneurysmal rupture dates in different patients and verify a temporal pattern in the occurrence of SAH.
  
  
  METHODS
  We analyzed a group of 563 patients with the exact aneurysm rupture dates, hospitalized at the Clinic of Neurosurgery, Clinical Center of Vojvodina, Novi Sad, Serbia, between January 1, 1998 and December 31, 2009. After the monthly distributions, we evaluated the period between two subsequent rupture dates.
  
  
  RESULTS
  The absolute number of SAH per month varied between 0 and 10. The monthly seasonal indices show a fluctuation of the time series (with the peak in March and nadir in September), but the median values of the number of aneurysm ruptures in a particular month did not differ significantly. The time scale of the aneurysm rupture dates shows that the most frequent interval between subsequent ruptures was 1 day (in 75 cases or 13.34%). Following this period, the number of days between ruptures showed a gradually decreasing pattern that could be approximated by exponential distribution.
  
  
  CONCLUSIONS
  The results are a clear confirmation that SAH patients do indeed present in clusters in a restricted population area. This exact clustering in our series is not particularly connected to month or season, yet strongly supports the existence of a temporal pattern in SAH occurrence.
authors.affiliation: Department of Neurosurgery, Clinical Centre of Vojvodina, H. Veljkova 1-10, 21000, Novi Sad, Serbia. pvulekovic@gmail.com
authors.forename: Petar
authors.initials: P
authors.lastname: Vuleković
authors.forename: Emilija
authors.initials: E
authors.lastname: Nikolić-Đorić
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Kojadinović
authors.forename: Vladimir
authors.initials: V
authors.lastname: Papić
authors.forename: Mladen
authors.initials: M
authors.lastname: Karan
authors.forename: Tamas
authors.initials: T
authors.lastname: Dóczi
mesh_terms: D017542:Aneurysm, Ruptured / Q000453:epidemiology*; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D015994:Incidence; D002532:Intracranial Aneurysm / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D012621:Seasons; D055771:Serbia; D013345:Subarachnoid Hemorrhage / Q000453:epidemiology*