title: Comparison of emergency department and hospital admissions data for air pollution time-series studies.
abstract: BACKGROUND
  Emergency department (ED) visit and hospital admissions (HA) data have been an indispensible resource for assessing acute morbidity impacts of air pollution. ED visits and HAs are types of health care visits with similarities, but also potentially important differences. Little previous information is available regarding the impact of health care visit type on observed acute air pollution-health associations from studies conducted for the same location, time period, outcome definitions and model specifications.
  
  
  METHODS
  As part of a broader study of air pollution and health in St. Louis, individual-level ED and HA data were obtained for a 6.5 year period for acute care hospitals in the eight Missouri counties of the St. Louis metropolitan area. Patient demographic characteristics and diagnostic code distributions were compared for four visit types including ED visits, HAs, HAs that came through the ED, and non-elective HAs. Time-series analyses of the relationship between daily ambient ozone and PM₂.₅ and selected cardiorespiratory outcomes were conducted for each visit type.
  
  
  RESULTS
  Our results indicate that, compared with ED patients, HA patients tended to be older, had evidence of greater severity for some outcomes, and had a different mix of specific outcomes. Consideration of 'HA through ED' appeared to more effectively select acute visits than consideration of 'non-elective HA'. While outcomes with the strongest observed temporal associations with air pollutants tended to show strong associations for all visit types, we found some differences in observed associations for ED visits and HAs. For example, risk ratios for the respiratory disease-ozone association were 1.020 for ED visits and 1.004 for 'HA through ED'; risk ratios for the asthma/wheeze-ozone association were 1.069 for ED visits and 1.106 for 'HA through ED'. Several factors (e.g. age) were identified that may be responsible, in part, for the differences in observed associations.
  
  
  CONCLUSIONS
  Demographic and diagnostic differences between visit types may lead to preference for one visit type over another for some questions and populations. The strengths of observed associations with air pollutants sometimes varied between different health care visit types, but the relative strengths of association generally were specific to the pollutant-outcome combination.
authors.affiliation: Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Road NE, Atlanta, GA 30322, USA. awinqui@emory.edu
authors.forename: A
authors.initials: A
authors.lastname: Winquist
authors.forename: M
authors.initials: M
authors.lastname: Klein
authors.forename: P
authors.initials: P
authors.lastname: Tolbert
authors.forename: W D
authors.initials: WD
authors.lastname: Flanders
authors.forename: J
authors.initials: J
authors.lastname: Hess
authors.forename: S E
authors.initials: SE
authors.lastname: Sarnat
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000633:toxicity; D000397:Air Pollution / Q000009:adverse effects*; D002318:Cardiovascular Diseases / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D010126:Ozone / Q000633:toxicity; D052638:Particulate Matter / Q000633:toxicity; D012140:Respiratory Tract Diseases / Q000453:epidemiology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone