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Heat-Related Deaths --- Chicago, Illinois, 1996--2001, and United States, 1979--1999

Heat waves (i.e., >3 consecutive days of air temperatures >90º F [>32.2º C]) are meteorologic events that contribute significantly to heat-related deaths. Exposure to excessive heat can cause illness, injury, and death. This report describes four cases of heat-related deaths*, as reported by the Office of the Medical Examiner, Cook County, Chicago, that occurred during 1996--2001; summarizes total heat-related deaths in Chicago during 1996--2001; and compares the number of heat-related deaths during the 1995 and 1999 Chicago heat waves. This report also summarizes trends in the United States during 1979--1999, describes risk factors associated with heat-related deaths and symptoms, and outlines preventive measures for heat-related illness, injury, and death. Persons at risk for heat-related death should reduce strenuous outdoor activities, drink water or nonalcoholic beverages frequently, and seek air conditioning.

Case Reports

Case 1. In June 1997, a woman aged 86 years with no known medical history was found unresponsive in her bedroom. Her grandson reported that the woman had kept the bedroom windows closed for a week and that the room was very hot. The room had no fan. Paramedics transported the woman to the hospital, where a rectal temperature of 108º F (42.2º C) was recorded. She was pronounced dead in the emergency department. An autopsy revealed moderate coronary atherosclerosis. Heat stroke was listed as the cause of death, with arteriosclerotic cardiovascular disease as a significant contributing condition.

Case 2. In July 1999, a woman aged 73 years whose medical history was unknown was found unresponsive behind a building. She had been seen earlier in the day drinking alcohol. Paramedics transported her to the hospital, where she was pronounced dead on arrival.

Her rectal temperature was registered as 108º F (42.2º C). An autopsy revealed a blood alcohol level of 117 mg/dL (legal blood alcohol limit in Illinois is 80 mg/dL) and a vitreous alcohol level of 157 mg/dL. The cause of death was listed as heat stroke.

Case 3. In March 2000, a man aged 35 years was found unresponsive in a steam room at a health club. Before entering the steam room, the man reportedly had slurred speech, and his hands were shaking. He was transported to the hospital, where he was pronounced dead on arrival. An autopsy documented previous hypertensive cerebral damage and a recent right basal ganglia infarct. The cause of death was listed as hyperthermia caused by hypertensive cardiovascular disease.

Case 4. In September 2000, a girl aged 5 months was found unresponsive in the back seat of her parents' car by her mother. The child had been left mistakenly in the car for 9 hours while her parents were at work. Paramedics transported the child to the hospital, where she was pronounced dead on arrival. The medical examiner listed the cause of death as heat stroke.

Summary of Heat-Related Deaths in Chicago and U.S. Trends

During the 1990s, Chicago experienced two heat waves. In July 1995, a heat wave resulted in 485 heat-related deaths and 739 excess deaths (4). An epidemiologic investigation of the heat wave identified advanced age and an inability to care for oneself as major risk factors for heat-related death (5). During 1999, a heat wave resulted in 103 heat-related deaths; 80 were attributed to extreme heat. Implementation of Chicago's Extreme Weather Operations Plan reduced the death toll by increasing the number of daily contacts for the elderly during the 1999 heat wave (6). During 1996--2001, annual totals of heat-related deaths across all age groups was highest in 1999 (Figure 1).

During 1979--1999, the most recent years for which national data are available, 8,015 deaths in the United States were heat-related. A total of 3,829 (48%) were "due to weather conditions," 377 (5%) were "of man-made origins" (e.g., heat generated in vehicles, kitchens, boiler rooms, furnace rooms, and factories), and 3,809 (48%) were "of unspecified origin" (7). An average of 182 deaths per year (range: 54--651) were associated with excessive heat resulting from weather conditions. Of the 3,764 (98%) weather-related deaths for which age of decedent was reported, 1,891 (49%) occurred among persons aged 15--64 years, 1,709 (45%) occurred among persons aged >65 years, and 164 (4%) occurred among children aged <15 years (7). During 1979--1999, rates for heat-related deaths increased with age (Figure 2).

Reported by: ER Donoghue, MD, Office of the Medical Examiner, Cook County, Chicago; M Nelson, PhD, G Rudis, MA, Office of Epidemiology, Illinois Dept of Public Health. RI Sabogal, MSPH, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; JT Watson, MD, G Huhn, MD, G Luber, PhD, EIS officers, CDC.

Editorial Note:

Exposure to high temperature for a sustained period can cause heat-related illness (hyperthermia) or death. The two most serious types of heat-related illness are heat exhaustion and heat stroke. Heat exhaustion is characterized by paleness, fatigue, muscle cramps, dizziness, headache, nausea or vomiting, and fainting. The skin is typically cool, and moistness and sweating might occur. The pulse rate is fast and weak, and breathing is fast and shallow. If untreated, heat exhaustion can progress to heat stroke (8). Heat stroke is a serious, often fatal condition characterized by a body temperature of >103º F (>39.4º C); red, hot, and dry skin (no sweating); rapid, strong pulse; throbbing headache; dizziness; nausea; confusion; and unconsciousness.

Elderly persons, children, and persons with certain medical conditions (e.g., heart disease) are at greatest risk for heat-related illness and death. Drinking alcohol, participating in strenuous outdoor physical activities in hot weather, and taking medications that reduce the body's ability to regulate its temperature or that inhibit perspiration also increase risk. Air conditioning is the most important protective factor against heat-related illness and death. For the 1995 and 1999 Chicago heat waves, the risk for heat-related death increased for persons with cardiac disease or psychiatric illness and for persons who lived alone. Having a working air conditioner and participating in group activities in which heat-related illness might be identified were the most important protective factors (5,6) (Box).

Heat-related morbidity and mortality could increase with periods of extreme heat (9). Many cities have developed emergency-response plans for heat waves. These response plans use information about risk factors and meteorologic conditions to implement prevention strategies that reduce morbidity and mortality from excessive heat (10). A heat-response plan also should recommend rolling energy blackouts in areas that use air conditioning to mitigate factors that increase the risk for heat-related morbidity and mortality. To defray energy costs, support of low-income populations might be necessary to allow the use of air-conditioning during summer months.


  1. Donoghue ER, Graham MA, Jentzen JM, Lifschultz BD, Luke JL, Mirchandani HG. National Association of Medical Examiners Ad Hoc Committee on the definition of heat-related fatalities: criteria for the diagnosis of heat-related deaths. Am J Forensic Med Pathol 1997;18:11--4.
  2. Kilbourne EM. Heat waves and hot environments. In: Noji EK, ed. The Public Health Consequences of Disasters. New York, New York: Oxford University Press, 1997:245--69.
  3. Kilbourne EM, Choi K, Jones TS, Thacker SB, Field Investigation Team. Risk factors for heat-stroke: a case-control study. JAMA 1982;247:3332--6.
  4. Whitman S, Good G, Donoghue ER, Benbow N, Shou W, Mou S. Mortality in Chicago attributed to the July 1995 heat wave. Am J Public Health 1997;87:1515--8.
  5. Semenza JC, Rubin CH, Falter KH, et al. Risk factors for heat-related mortality during the July 1995 heat wave in Chicago. N Engl J Med 1996;35:84--90.
  6. Naughton MP, Henderson A, Mirabelli MC, et al. Heat-related mortality during a 1999 heat wave in Chicago. Am J Prev Med 2002;22:221--7.
  7. National Center for Health Statistics. Compressed mortality file. Hyattsville, Maryland: U.S. Department of Health and Human Services, CDC, 2002.
  8. CDC. Extreme heat. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC, 1996. Available at
  9. Gaffen DJ. Increased summertime heat stress in the US. Nature 1998;396:529--30.
  10. McGeehin MA, Mirabelli M. The potential impacts of climate variability and change on temperature-related morbidity and mortality in the United States. Environ Health Perspect 2001;109:185--90.

* Defined as one in which exposure to high ambient temperatures either caused the death or contributed to it substantially, body temperature at the time of collapse was >105º F (>40.6º C), the decedent had a history of exposure to high ambient temperature, and other causes of hyperthermia could reasonably be excluded (1). Because rates of death from other causes (e.g., cardiovascular and respiratory disease) increase during heat waves (2,3), deaths classified as caused by hyperthermia represent only a portion of heat-related mortality.

During 1979--1998, the underlying cause of death attributed to excessive heat exposure was classified according to the International Classification of Diseases, Ninth Revision (ICD-9), code E900.0, "due to weather conditions"; code E900.1, "of man-made origins"; and code E900.9, "of unspecified origin." Data for 1999 were obtained from ICD-10; code X30, "exposure to excessive natural heat (deaths)," was added to the 1979--1998 ICD-9 code E900.0, "excessive heat due to weather conditions (deaths)." Data were obtained from the Compressed Mortality File of CDC's National Center for Health Statistics, which contains information from death certificates filed in the 50 states and the District of Columbia.

Figure 1

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Figure 2

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Box 3
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