Increased hospital admissions associated with extreme-heat exposure in King County, Washington, 1990–2010

Tania Busch Isaksen, Michael G. Yost, Elizabeth K. Hom, You Ren, Hilary Lyons and Richard A. Fenske


Increased morbidity and mortality have been associated with extreme heat events, particularly in temperate climates. Few epidemiologic studies have considered the impact of extreme heat events on hospitalization rates in the Pacific Northwest region. This study quantifies the historic (May to September 1990–2010) heat-morbidity relationship in the most populous Pacific Northwest County, King County, Washington. A relative risk (RR) analysis was used to explore the association between heat and all non-traumatic hospitalizations on 99th percentile heat days, whereas a time series analysis using a piecewise linear model approximation was used to estimate the effect of heat intensity on hospitalizations, adjusted for temporal trends and day of the week. A non-statistically significant 2% [95% CI: 1.02 (0.98, 1.05)] increase in hospitalization risk, on a heat day vs. a non-heat day, was noted for all-ages and all non-traumatic causes. When considering the effect of heat intensity on admissions, we found a statistically significant 1.59% (95% CI: 0.9%, 2.29%) increase in admissions per degree increase in humidex above 37.4°C. Admissions stratified by cause and age produced statistically significant results with both relative risk and time series analyses for nephritis and nephrotic syndromes, acute renal failure, and natural heat exposure hospitalizations. This study demonstrates that heat, expressed as humidex, is associated with increased hospital admissions. When stratified by age and cause of admission, the non-elderly age groups (<85 years) experience significant risk for nephritis and nephrotic syndromes, acute renal failure, natural heat exposure, chronic obstructive pulmonary disease, and asthma hospitalizations.

  • 1.

    IPCC (Intergovernmental Panel on Climate Change). Climate Change 2013. The Physical Science Basis. Working Group 1 Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Summary for Policymakers. Switzerland: Intergovernmental Panel on Climate Change. 2013. Available at:

  • 2.

    Whitman S, Good G, Donoghue ER, Benbow N, Shou W, et al. Mortality in Chicago attributed to the July 1995 heat wave. Am J Public Health 1997;87(9):1515–8.

  • 3.

    Naughton M. Heat-related mortality during a 1999 heat wave in Chicago. Am J Prev Med 2002;22(4):221–7.

  • 4.

    Baccini M, Biggeri A, Accetta G, Kosatsky T, Katsouyanni K, et al. Heat effects on mortality in 15 European cities. Epidemiology (Cambridge, Mass.) 2008;19(5):711–9.

  • 5.

    Basu R, Feng WY, Ostro BD. Characterizing temperature and mortality in nine California counties. Epidemiology (Cambridge, Mass.) 2008;19(1):138–45.

  • 6.

    Anderson BG, Bell ML. Weather-related mortality: how heat, cold, and heat waves affect mortality in the United States. Epidemiology (Cambridge, Mass.) 2009;20(2):205–13.

  • 7.

    Jackson JE, Yost MG, Lamb BK, Lamb BK, Chung SH, et al. Public health impacts of climate change in Washington State: projected mortality risks due to heat events and air pollution. Climatic Change 2010;102:1–2.

  • 8.

    Anderson BG, Bell ML. Heat waves in the United States: mortality risk during heat waves and effect modification by heat wave characteristics in 43 U.S. communities. Environ Health Perspect 2011;119(2):210–8.

  • 9.

    Semenza JC. Acute renal failure during heat waves. Am J Prev Med 1999;17:1.

  • 10.

    Semenza JC, McCullough JE, Flanders D, McGeehin MA, Lumpkin JR. Excess hospital admissions during the July 1995 heat wave in Chicago. Am J Prev Med 1999;16:269–77.

  • 11.

    Mastrangelo G, Fedeli U, Visentin C, Milan G, Fadda E, et al. Pattern and determinants of hospitalization during heat waves: an ecologic study. BMC Public Health 2007;7:200.

  • 12.

    Knowlton K, Rotkin-Ellman M, King G, Margolis HG, Smith D, et al. The 2006 California heat wave: impacts on hospitalizations and emergency department visits. Environ Health Perspect 2009;117(1):61–7.

  • 13.

    Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Pub Health 2008;29(1):41–55.

  • 14.

    Fletcher BA, Lin S, Fitzgerald EF, Hwang SA. Association of summer temperatures with hospital admissions for renal diseases in New York State: a case-crossover study. Am J Epidemiol 2012;175(9):907–16.

  • 15.

    Ostro B, Rauch S, Green R, Malig B, Basu R. The effects of temperature and use of air conditioning on hospitalizations. Am J Epidemiol 2010;172(9):1053–61.

  • 16.

    Lin S, Luo M, Walker RJ, Liu X, Hwang SA, et al. Extreme high temperatures and hospital admissions for respiratory and cardiovascular diseases. Epidemiology (Cambridge, Mass.) 2009;20(5):738–46.

  • 17.

    Koken PJ, Piver WT, Ye F, Elixhauser A, Olsen LM, et al. Temperature, air pollution, and hospitalization for cardiovascular diseases among elderly people in Denver. Environ Health Perspect 2003;111(10):1312–7.

  • 18.

    Green RS, Basu R, Malig B, Broadwin R, Kim JJ, et al. The effect of temperature on hospital admissions in nine California counties. Int J Pub Health 2010;55(2):113–21.

  • 19.

    Kaiser R, Rubin CH, Henderson AK, Wolfe MI, Kieszak S, et al. Heat-related death and mental illness during the 1999 Cincinnati heat wave. Am J Forensic Med Pathol 2001;22(3): 303–7.

  • 20.

    Jones TS, Liang AP, Kilbourne EM, Griffin MR, Patriarca PA, et al. Morbidity and mortality associated with the July 1980 heat wave in St Louis and Kansas City, Mo. J Am Med Assoc 1982;247(24):3327–31.

  • 21.

    O’Neill MS, Zanobetti A, Schwartz J. Modifiers of the temperature and mortality association in seven US cities. Am J Epidemiol 2003;157(12):1074–82.

  • 22.

    O’Neill MS, Zanobetti A, Schwartz J. Disparities by race in heat-related mortality in four US cities: the role of air conditioning prevalence. J Urban Health 2005;82(2):191–7.

  • 23.

    King County. (Updated December 21, 2012) About King County and its Government. Avialable at: Accessed on September 23, 2013.

  • 24.

    Isaksen TB, Yost M, Hom E, Fenske R. Projected health impacts of heat events in Washington State associated with climate change. Rev Environ Health 2014;29:1–2.

  • 25.

    Cheng CS, Campbell M, Li Q, Li G, Auld H, et al. Differential and Combined Impacts of Winter and Summer Weather and Air Pollution due to Global Warming on Human Mortality in South-central Canada (6795-15-2001/4400011). Toronto, Canada: Health Canada, Health Policy Research Program. 2005. Avialable at: Accessed 10 November 2013.

  • 26.

    Washington State Department of Health, Office of Hospital and Patient Data Systems. April 2, 2010. Procedure manual for submitting discharge data for UB-04. Olympia, WA:Center for Health Statistics, Hospital and Patient Data Systems, Comprehensive Hospital Abstract Reporting System (CHARS). Avialable at:

  • 27.

    Hansen AL, Bi P, Ryan P, Nitschke M, Pisaniello D, et al. The effect of heat waves on hospital admissions for renal disease in a temperate city of Australia. Int J Epidemiol 2008;37(6):1359–65.

  • 28.

    Reid CE, Mann JK, Alfasso R, English PB, King GC, et al. Evaluation of a Heat Vulnerability Index on Abnormally Hot Days: An Environmental Public Health Tracking Study. Environmental Health Perspectives 2012;120(5):715–720.

  • 29.

    Lin S, Hsu WH, Van ZAR, Saha S, Luber G, et al. Excessive heat and respiratory hospitalizations in New York State: estimating current and future public health burden related to climate change. Environmental Health Perspectives 2012;120(11):1571–7.

  • 30.

    Washington State Office of Financial Management. King County Census Data. 2012. Avialable at:

  • 31.

    Maurer EP, Wood AW, Adam JC, Lettenmaier DP, Nijssen B. A long-term hydrologically based data set of land surface fluxes and states for the conterminous United States. J Climate 2002;15:3237–325.

  • 32.

    “PRISM Climate Group, Oregon State U.” PRISM Climate Group, Oregon State U. N.p., n.d. Web. 15 Feb. 2014.

  • 33.

    Busch Isaksen T, Fenske R, Hom E, Ren Y, Lyons H, et al. Increased mortality associated with extreme-heat exposure in King County, Washington, 1980-2010. Int J Biometeorol (accepted for publication) 2014.

  • 34.

    Masterton JM, Richardson FA. A method of quantifying human discomfort due to heat and humidity. Downsview, Ontario, Canada: AES, Environment Canada, CLI, 1979.

  • 35.

    Canadian Centre for Occupational Health and Safety. 2011-07-04. Humidex Rating and Work. Available at: ed. Canada: Canadian Centre for Occupational Health and Safety.

  • 36.

    R Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, 2012. Avialable at:

  • 37.

    Schwartz J. Who is sensitive to extremes of temperature? A case-only analysis. Epidemiology 2005;16(1):67–7.

  • 38.

    Daniela DI, Paola M, Claudia M, Francesca D, Bettina M, et al. The impact of heat waves on mortality in 9 European cities: results from the EuroHEAT project. Environ Health 2010;9:37.

  • 39.

    Kalkstein LS, Greene JS. Quantitative analysis of summer air masses in the eastern United States and an application to human mortality. Climate Res 1996;7:43–53.

  • 40.

    Kalkstein LS, Greene S, Mills DM, Samenow J. An evaluation of the progress in reducing heat-related human mortality in major U.S. cities. Nat Hazards 2011;56(1):113–29.

  • 41.

    Morabito M, Crisci A, Grifoni D, Orlandini S, Cecchi L, et al. Winter air-mass-based synoptic climatological approach and hospital admissions for myocardial infarction in Florence, Italy. Environ Res 2006;102(1):52–60.

  • 42.

    Armstrong B. Models for the relationship between ambient temperature and daily mortality. Epidemiology 2006;17(6):624–31.

  • 43.

    Gasparrini A. Distributed lag linear and non-linear models in R: the package dlnm. J Stat Software 2011;43(8):1–20.

  • 44.

    Sheridan SC, Kalkstein AJ, Kalkstein LS. Trends in heat-related mortality in the United States, 1975-2004. Nat Hazards 2009;50(1):145–60.

  • 45.

    Sheridan S. Spatial Synoptic Classification. Kent State University. Department of Geography. 2013. Available at:

  • 46.

    Kovats RS, Hajat S, Wilkinson P. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK. Occup Environ Med 2004;61(11):893–8.

  • 47.

    Linares C, Díaz J. Impact of high temperatures on hospital admissions: comparative analysis with previous studies about mortality (Madrid). Eur J Public Health 2008;18(3):317–22.

  • 48.

    Li B, Sain S, Mearns LO, Anderson HA, Bekkedal MYV, et al. The impact of extreme heat on morbidity in Milwaukee, Wisconsin. Climatic Change 2012;110:959–76.

  • 49.

    Michelozzi P, Accetta G, De SM, D’Ippoliti D, Marino C, PHEWE Collaborative Group. High temperature and hospitalizations for cardiovascular and respiratory causes in 12 European cities. Am J Res Crit Care 2009;179(5):383–9.

  • 50.

    Medina-Ramón M, Zanobetti A, Cavanagh DP, Schwartz, J. Extreme temperatures and mortality: assessing effect modification by personal characteristics and specific cause of death in a multi-city case-only analysis. Environmental Health Perspectives 2006;114(9):1331–6.

  • 51.

    United States Renal Data System. USRDS 2007 Annual Data Report. Bethesda, MD: National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services, 2007.

  • 52.

    “Public Health – Seattle & King County.” Indicator: Diabetes Prevalence, King County. Public Health – Seattle King County, 12 Aug. 2013. Available at:

  • 53.

    Hamlet AF, Lee SY, Mickelson KEB, McGuire Elsner M. Effects of projected climate change on energy supply and demand in the Pacific Northwest and Washington State. Chapter 4 in The Washington climate change impacts assessment: evaluating Washington’s Future in a Changing Climate, Climate Impacts Group, University of Washington, Seattle, Washington. 2009. Available at:

  • 54.

    Curriero FC, Heiner KS, Samet JM, Zeger SL, Strug L, et al. Temperature and mortality in 11 cities of the eastern United States. Am J Epidemiol 2002;155(1):80–7.

  • 55.

    Buckley JP, Samet JM, Richardson DB. Commentary: does air pollution confound studies of temperature?. Epidemiology (Cambridge, Mass.) 2014;25(2):242–5.

  • 56.

    Zanobetti A, Schwartz J. Temperature and mortality in nine US cities. Epidemiology (Cambridge, Mass.) 2008;19(4):563–70.

  • 57.

    Koepsell TD, Weiss NS. Epidemiologic methods: studying the occurrence of illness. Oxford: Oxford University Press, 2003.

Purchase article
Get instant unlimited access to the article.
Price including VAT
Log in
Already have access? Please log in.

Journal + Issues

Reviews on Environmental Health is an international quarterly periodical that fills the need for rapid publication of specialized comprehensive review articles on hot topics in the field of environmental health. The journal is an inspiring forum for scientists, environmentalists, physicians, engineers and students active in the area of public health, including quality of life.