title: Population density predicts outcome from out-of-hospital cardiac arrest in Victoria, Australia.
abstract: OBJECTIVE
  To examine the impact of population density on incidence and outcome of out-of-hospital cardiac arrest (OHCA).
  
  
  METHODS
  Data were extracted from the Victorian Ambulance Cardiac Arrest Registry for all adult OHCA cases of presumed cardiac aetiology attended by the emergency medical service (EMS) between 1 January 2003 and 31 December 2011. Cases were allocated into one of five population density groups according to their statistical local area: very low density (≤ 10 people/km(2)), low density (11-200 people/km(2)), medium density (201-1000 people/km(2)), high density (1001-3000 people/km(2)), and very high density (> 3000 people/km(2)).
  
  
  METHODS
  Survival to hospital and survival to hospital discharge.
  
  
  RESULTS
  The EMS attended 27 705 adult presumed cardiac OHCA cases across 204 Victorian regions. In 12 007 of these (43.3%), resuscitation was attempted by the EMS. Incidence was lower and arrest characteristics were consistently less favourable for lower population density groups. Survival outcomes, including return of spontaneous circulation, survival to hospital and survival to hospital discharge, were significantly poorer in less densely populated groups (P < 0.001 for all comparisons). When compared with very low density populations, the risk-adjusted odds ratios of surviving to hospital discharge were: low density, 1.88 (95% CI, 1.15-3.07); medium density, 2.49 (95% CI, 1.55-4.02); high density, 3.47 (95% CI, 2.20-5.48) and very high density, 4.32 (95% CI, 2.67-6.99).
  
  
  CONCLUSIONS
  Population density is independently associated with survival after OHCA, and significant variation in the incidence and characteristics of these events are observed across the state.
authors.affiliation: Ambulance Victoria, Melbourne, VIC, Australia. ziad.nehme@ambulance.vic.gov.au.
authors.forename: Ziad
authors.initials: Z
authors.lastname: Nehme
authors.affiliation: Ambulance Victoria, Melbourne, VIC, Australia.
authors.forename: Emily
authors.initials: E
authors.lastname: Andrew
authors.affiliation: Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, Australia.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Cameron
authors.affiliation: Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, Australia.
authors.forename: Janet E
authors.initials: JE
authors.lastname: Bray
authors.affiliation: Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC, Australia.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Bernard
authors.affiliation: Department of Medicine, Monash University, Melbourne, VIC, Australia.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Meredith
authors.affiliation: Discipline of Emergency Medicine, University of Western Australia, Perth, WA, Australia.
authors.forename: Karen
authors.initials: K
authors.lastname: Smith
mesh_terms: D000328:Adult; D004632:Emergency Medical Services; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000453:epidemiology* / Q000401:mortality; D017063:Outcome Assessment, Health Care; D011156:Population Density; D012042:Registries / Q000706:statistics & numerical data; D012189:Retrospective Studies; D015996:Survival Rate; D014739:Victoria / Q000453:epidemiology