title: Airborne Fine Particles and Risk of Hospital Admissions for Understudied Populations: Effects by Urbanicity and Short-Term Cumulative Exposures in 708 U.S. Counties.
abstract: Evidence of health risks associated with ambient airborne fine particles in nonurban populations is extremely limited.
  
  
  
  We estimated the risk of hospitalization associated with short-term exposures to particulate matter with an aerodynamic diameter < 2.5 μm (PM2.5) in urban and nonurban counties with population ≥ 50,000.
  
  
  
  We utilized a database of daily cardiovascular- and respiratory-related hospitalization rates constructed from Medicare National Claims History files (2002-2006), including 28 million Medicare beneficiaries in 708 counties. Daily PM2.5exposures were estimated using the Community Multiscale Air Quality (CMAQ) downscaler. We used time-series analysis of hospitalization rates and PM2.5to evaluate associations between PM2.5levels and hospitalization risk in single-pollutant models.
  
  
  
  We observed an association between cardiovascular hospitalizations and same-day PM2.5with higher risk in urban counties: 0.35% [95% posterior interval (PI): -0.71%, 1.41%] and 0.98% (95% PI: 0.73%, 1.23%) increases in hospitalization risk per 10-μg/m3increment in PM2.5were observed in the least-urban and most-urban counties, respectively. The largest association for respiratory hospitalizations, a 2.57% (95% PI: 0.87%, 4.30%) increase per 10-μg/m3increase in PM2.5, was observed in the least-urban counties; in the most-urban counties, a 1.13% (0.73%, 1.54%) increase was observed. Effect estimates for cardiovascular hospitalizations were highest for smaller lag times, whereas effect estimates for respiratory hospitalizations increased as more days of exposure were included.
  
  
  
  In nonurban counties with population ≥ 50,000, exposure to PM2.5is associated with increased risk for respiratory hospitalizations; in urban counties, exposure is associated with increased risk of cardiovascular hospitalizations. Effect estimates based on a single day of exposure may underestimate true effects for respiratory hospitalizations.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, USA.
authors.forename: Mercedes A
authors.initials: MA
authors.lastname: Bravo
authors.forename: Keita
authors.initials: K
authors.lastname: Ebisu
authors.forename: Francesca
authors.initials: F
authors.lastname: Dominici
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.forename: Roger D
authors.initials: RD
authors.lastname: Peng
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Bell
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data*; D002318:Cardiovascular Diseases / Q000453:epidemiology; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D006760:Hospitalization / Q000706:statistics & numerical data*; D052638:Particulate Matter / Q000032:analysis*; D012140:Respiratory Tract Diseases / Q000453:epidemiology; D018570:Risk Assessment; D014481:United States
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter