title: Spatial variation in hyperthermia emergency department visits among those with employer-based insurance in the United States - a case-crossover analysis.
abstract: BACKGROUND
  Predictions of intense heat waves across the United States will lead to localized health impacts, most of which are preventable. There is a need to better understand the spatial variation in the morbidity impacts associated with extreme heat across the country to prevent such adverse health outcomes.
  
  
  METHODS
  Hyperthermia-related emergency department (ED) visits were obtained from the Truven Health MarketScan(®) Research dataset for 2000-2010. Three measures of daily ambient heat were constructed using meteorological observations from the National Climatic Data Center (maximum temperature, heat index) and the Spatial Synoptic Classification. Using a time-stratified case crossover approach, odds ratio of hyperthermia-related ED visit were estimated for the three different heat measures. Random effects meta-analysis was used to combine the odds ratios for 94 Metropolitan Statistical Areas (MSA) to examine the spatial variation by eight latitude categories and nine U.S. climate regions.
  
  
  RESULTS
  Examination of lags for all three temperature measures showed that the odds ratio of ED visit was statistically significant and highest on the day of the ED visit. For heat waves lasting two or more days, additional statistically significant association was observed when heat index and synoptic classification was used as the temperature measure. These results were insensitive to the inclusion of air pollution measures. On average, the maximum temperature on the day of an ED visit was 93.4°F in 'South' and 81.9°F in the 'Northwest' climatic regions of United States. The meta-analysis showed higher odds ratios of hyperthermia ED visit in the central and the northern parts of the country compared to the south and southwest.
  
  
  CONCLUSIONS
  The results showed spatial variation in average temperature on days of ED visit and odds ratio for hyperthermia ED visits associated with extreme heat across United States. This suggests that heat response plans need to be customized for different regions and the potential role of hyperthermia ED visits in syndromic surveillance for extreme heat.
authors.affiliation: Climate and Health Program, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, 30341, GA, USA. ssaha@cdc.gov.
authors.forename: Shubhayu
authors.initials: S
authors.lastname: Saha
authors.affiliation: Departments of Chemistry and Environmental Studies, Warren Wilson College, PO Box 9000, CPO 6066, Asheville, 28815, NC, USA. jbrock@warren-wilson.edu.
authors.forename: John W
authors.initials: JW
authors.lastname: Brock
authors.affiliation: Environmental Health Tracking Branch, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, 30341, GA, USA. dvq3@cdc.gov.
authors.forename: Ambarish
authors.initials: A
authors.lastname: Vaidyanathan
authors.affiliation: National Climatic Data Center, Asheville, 28801, NC, USA. david.easterling@noaa.gov.
authors.forename: David R
authors.initials: DR
authors.lastname: Easterling
authors.affiliation: Climate and Health Program, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, 30341, GA, USA. gcl4@cdc.gov.
authors.forename: George
authors.initials: G
authors.lastname: Luber
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D018592:Cross-Over Studies; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D055874:Extreme Heat / Q000009:adverse effects*; D005334:Fever / Q000453:epidemiology* / Q000209:etiology; D006264:Health Benefit Plans, Employee / Q000706:statistics & numerical data; D016017:Odds Ratio; D010126:Ozone / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D012307:Risk Factors; D012621:Seasons; D013997:Time Factors; D014481:United States / Q000453:epidemiology
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone