title: Cause-specific risk of hospital admission related to extreme heat in older adults.
abstract: OBJECTIVE
  Heat exposure is known to have a complex set of physiological effects on multiple organ systems, but current understanding of the health effects is mostly based on studies investigating a small number of prespecified health outcomes such as cardiovascular and respiratory diseases.
  
  
  OBJECTIVE
  To identify possible causes of hospital admissions during extreme heat events and to estimate their risks using historical data.
  
  
  METHODS
  Matched analysis of time series data describing daily hospital admissions of Medicare enrollees (23.7 million fee-for-service beneficiaries [aged ≥65 years] per year; 85% of all Medicare enrollees) for the period 1999 to 2010 in 1943 counties in the United States with at least 5 summers of near-complete (>95%) daily temperature data.
  
  
  METHODS
  Heat wave periods, defined as 2 or more consecutive days with temperatures exceeding the 99th percentile of county-specific daily temperatures, matched to non-heat wave periods by county and week.
  
  
  METHODS
  Daily cause-specific hospitalization rates by principal discharge diagnosis codes, grouped into 283 disease categories using a validated approach.
  
  
  RESULTS
  Risks of hospitalization for fluid and electrolyte disorders, renal failure, urinary tract infection, septicemia, and heat stroke were statistically significantly higher on heat wave days relative to matched non-heat wave days, but risk of hospitalization for congestive heart failure was lower (P < .05). Relative risks for these disease groups were 1.18 (95% CI, 1.12-1.25) for fluid and electrolyte disorders, 1.14 (95% CI, 1.06-1.23) for renal failure, 1.10 (95% CI, 1.04-1.16) for urinary tract infections, 1.06 (95% CI, 1.00-1.11) for septicemia, and 2.54 (95% CI, 2.14-3.01) for heat stroke. Absolute risk differences were 0.34 (95% CI, 0.22-0.46) excess admissions per 100,000 individuals at risk for fluid and electrolyte disorders, 0.25 (95% CI, 0.12-0.39) for renal failure, 0.24 (95% CI, 0.09-0.39) for urinary tract infections, 0.21 (95% CI, 0.01-0.41) for septicemia, and 0.16 (95% CI, 0.10-0.22) for heat stroke. For fluid and electrolyte disorders and heat stroke, the risk of hospitalization increased during more intense and longer-lasting heat wave periods (P < .05). Risks were generally highest on the heat wave day but remained elevated for up to 5 subsequent days.
  
  
  CONCLUSIONS
  Among older adults, periods of extreme heat were associated with increased risk of hospitalization for fluid and electrolyte disorders, renal failure, urinary tract infection, septicemia, and heat stroke. However, the absolute risk increase was small and of uncertain clinical importance.
authors.affiliation: Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Jennifer F
authors.initials: JF
authors.lastname: Bobb
authors.affiliation: Department of Emergency Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Ziad
authors.initials: Z
authors.lastname: Obermeyer
authors.affiliation: Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Francesca
authors.initials: F
authors.lastname: Dominici
mesh_terms: D000368:Aged; D055874:Extreme Heat / Q000009:adverse effects*; D005260:Female; D006333:Heart Failure / Q000453:epidemiology; D018883:Heat Stroke / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D006278:Medicare; D051437:Renal Insufficiency / Q000453:epidemiology; D012306:Risk; D012621:Seasons; D018805:Sepsis / Q000453:epidemiology; D014481:United States; D014552:Urinary Tract Infections / Q000453:epidemiology; D014883:Water-Electrolyte Imbalance / Q000453:epidemiology