title: Geographic distribution of trauma centers and injury-related mortality in the United States.
abstract: BACKGROUND
  Regionalized trauma care improves outcomes; however, access to care is not uniform across the United States. The objective was to evaluate whether geographic distribution of trauma centers correlates with injury mortality across state trauma systems.
  
  
  METHODS
  Level I or II trauma centers in the contiguous United States were mapped. State-level age-adjusted injury fatality rates per 100,000 people were obtained and evaluated for spatial autocorrelation. Nearest neighbor ratios (NNRs) were generated for each state. A NNR less than 1 indicates clustering, while a NNR greater than 1 indicates dispersion. NNRs were tested for difference from random geographic distribution. Fatality rates and NNRs were examined for correlation. Fatality rates were compared between states with trauma center clustering versus dispersion. Trauma center distribution and population density were evaluated. Spatial-lag regression determined the association between fatality rate and NNR, controlling for state-level demographics, population density, injury severity, trauma system resources, and socioeconomic factors.
  
  
  RESULTS
  Fatality rates were spatially autocorrelated (Moran's I = 0.35, p < 0.01). Nine states had a clustered pattern (median NNR, 0.55; interquartile range [IQR], 0.48-0.60), 22 had a dispersed pattern (median NNR, 2.00; IQR, 1.68-3.99), and 10 had a random pattern (median NNR, 0.90; IQR, 0.85-1.00) of trauma center distribution. Fatality rate and NNR were correlated (ρ = 0.34, p = 0.03). Clustered states had a lower median injury fatality rate compared with dispersed states (56.9 [IQR, 46.5-58.9] vs. 64.9 [IQR, 52.5-77.1]; p = 0.04). Dispersed compared with clustered states had more counties without a trauma center that had higher population density than counties with a trauma center (5.7% vs. 1.2%, p < 0.01). Spatial-lag regression demonstrated that fatality rates increased by 0.02 per 100,000 persons for each unit increase in NNR (p < 0.01).
  
  
  CONCLUSIONS
  Geographic distribution of trauma centers correlates with injury mortality, with more clustered state trauma centers associated with lower fatality rates. This may be a result of access relative to population density. These results may have implications for trauma system planning and require further study to investigate underlying mechanisms.
  
  
  METHODS
  Therapeutic/care management study, level IV.
authors.affiliation: From the Division of General Surgery and Trauma, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Brown
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Rosengart
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Billiar
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Peitzman
authors.forename: Jason L
authors.initials: JL
authors.lastname: Sperry
mesh_terms: D005843:Geography; D017052:Hospital Mortality; D006801:Humans; D014193:Trauma Centers / Q000600:supply & distribution*; D014481:United States / Q000453:epidemiology; D014947:Wounds and Injuries / Q000401:mortality*