In the summer of 1995, the Midwestern United States experienced a severe heat wave. Medical examiners in Milwaukee and Chicago encountered hundreds of heat-related deaths (1,2). A similar heat-related outbreak occurred in Philadelphia in 1993 (3,4). Because of the many fatalities that occurred during these epidemics, questions arose about the criteria that medical examiners use for evaluating and certifying potential heat-related deaths.
In Philadelphia, deaths were determined to be heat-related if (a) there was a documented antemortem core temperature of ≥105°F (≥40.6°C) or (b) the body was found in an enclosed environment with high ambient temperature without adequate cooling devices and the individual had been known to be alive at the onset of the heat wave (4). In Milwaukee, deaths were certified as heat-related if (a) the decedent's measured body temperature was ≥105°F (≥40.6°C) or (b) there was evidence of high environmental temperature-usually ≥100°F (≥37.7°C)-at the scene of the death (2). In Chicago, deaths that met one of the following three criteria were classified as heat-related: (a) a measured body temperature of ≥105°F (≥40.6°C) at the time of death or immediately after death, (b) substantial environmental or circumstantial evidence of heat as a contributor to death (e.g., decedent found in a room without air conditioning, all windows closed, and a high ambient temperature), or (c) a decedent found in a decomposed condition without evidence of other cause of death who was last seen alive during the heat wave period (1).
The Centers for Disease Control and Prevention (CDC), after reviewing the Philadelphia and Chicago epidemics and the diagnostic criteria employed, found that medical examiners had properly certified deaths as heat-related. On both occasions, the CDC noted the need for uniform criteria for heat-related deaths (1,3).
SELECTED ILLUSTRATIVE CASES
During July 12-16, 1995, Chicago experienced one of the deadliest heat waves in the city's history. The heat index, a combination of heat and humidity, topped 100°F (37.8°C) daily and surpassed 115°F (46.1°C) on two consecutive days (5). Recurrent periods of intense heat followed the initial heat wave. Those at greatest risk of dying from the heat were elderly people and those with medical illnesses who were socially isolated and did not have access to air conditioning (6). The following illustrative cases are selected from over 628 heat-related deaths occurring during the summer of 1995 in Cook County, IL.
At 4:00 P.M. on July 14, 1995, two 3-year-old boys were found comatose in the rear of a sport utility vehicle. The windows of the vehicle were closed and the engine was off. A day-care worker had left the children in the vehicle when she returned from an outing with seven other children at 2:00 P.M. Both boys were pronounced dead in the emergency room 1 h after being found. Their rectal temperatures were 107°F (41.7°C) and 108°F (42.2°C). Both children showed cerebral edema and petechial hemorrhages over the heart, lungs, and thymus gland. One child showed hemorrhage in the right retroperitoneal tissues and over the surface of the colon. The other child showed extensive hemorrhage in the right middle and lower lobes of the lung. Both deaths were certified as heat stroke.
At 8:45 P.M. on July 14, 1995, an 89-year-old man was found dead in the bedroom by his wife. The temperature in the bedroom was over 100°F (37.8°C), and the electricity in the home had been out for 5 h because of a power failure. Tardieu spots were present on the upper chest and bruises on both knees. The cause of death was certified as arteriosclerotic cardiovascular disease, and heat stress was listed as a significant contributing condition.
At 9:15 P.M. on July 16, 1995, a 76-year-old man was found dead, in a moderate state of decomposition, in the kitchen of his second-floor apartment. He was last seen alive at 4:30 P.M. on July 14, 1995. A dead dog was also present in the apartment. The windows were closed and no air conditioning or fans were present. The cause of death was certified as arteriosclerotic cardiovascular disease, and heat stress was listed as a significant contributing condition.
At 5:00 P.M. on July 23, 1995, an 85-year-old woman and her 65-year-old son were found dead in their apartment. They were last seen alive on July 13, 1995. The apartment was very humid. The windows were closed and no air conditioning or fans were present. Both bodies showed advanced decomposition, mummification, and maggot infestation. The son's body showed partial skeletonization of the face. Both deaths were certified as arteriosclerotic cardiovascular disease, and heat stress was listed as a significant contributing condition.
At 1:45 P.M. on August 12, 1995, a 37-year-old man was found dead in his closed automobile. He was last seen alive at 11:30 A.M. that day, when he was observed sitting in the front seat hitting his head against the windshield. The ignition was in the "on" position, but the engine was not running. The air conditioner was in the "on" position. The automobile would not start. The maximum outdoor temperature for the day was 98°F (36.7°C). The body was warm to touch and the rectal temperature was 107.4°F (41.9°C). The upper extremities showed skin slippage. Multiple recent bruises were present over the lower extremities. The heart showed moderate coronary atherosclerosis, with 50% occlusion of the left anterior descending coronary artery. The liver was fatty. The lungs and spleen were congested. The blood alcohol was 275 mg/dl. Blood carbon monoxide and benzoylecgonine were negative. The cause of death was certified as heat stroke, and alcohol intoxication was listed as a significant contributing condition.
Victims of heat stroke who are brought alive to medical facilities display mental status abnormalities and high body temperatures, usually ≥105°F (≥40.6°C). They typically show rapid heart rates, rapid respirations, and normal or low blood pressure. In virtually all cases of heat stroke, liver and muscle enzymes will be elevated (7). Complications include adult respiratory distress syndrome, kidney failure, liver failure, rhabdomyolysis, and disseminated intravascular coagulation (8). Although the initial recorded temperature is usually greater than 105°F (40.6°C), normal or subnormal temperature may be seen if cooling has been attempted prior to arrival at the hospital (7). The deaths of these patients do not usually present diagnostic or certification problems.
The diagnosis of heat-related death in persons found dead is more difficult. Medical examiners should consider the possibility that death may be heat-related in any person exposed to high levels of heat. A sudden increase in mortality during a period of intense heat should also raise this consideration. Autopsy findings are nonspecific but may include petechial or larger hemorrhages over the surface of the body, petechial hemorrhages over the lungs, pulmonary edema, and cerebral edema (9). Often, the body may be found in an advanced state of decomposition, further complicating the diagnostic problem.
Elevated ambient temperature can cause a rapid, dramatic rise in deaths, nearly all of which are preventable. Medical examiners need to be alert to the possibility that heat-related deaths may be occurring in their communities so that lifesaving preventive measures may be promptly implemented (10,11).
Lack of a uniform definition for heat-related death has produced wide variation in the criteria used to certify these deaths. The most stringent definition of heat-related death requires an antemortem body temperature of ≥105°F (≥40.6°C) without other reasonable explanation. This definition precludes certifying any death as heat-related if the body temperature was not measured and drastically underestimates heat-related mortality (1). The use of this definition in the Philadelphia (4) and Chicago epidemics would have identified less than 13% of the excess deaths due to heat. At the other extreme, certifying all deaths occurring during a heat wave as heat-related would overestimate this mortality. A simple, easy to use, middle-ground definition is needed.
The National Association of Medical Examiners Ad Hoc Committee on the Definition of Heat-Related Fatalities recommends the following definition of "heat-related death": a death in which exposure to high ambient temperature either caused the death or significantly contributed to it. The committee also recommends that the diagnosis of heat-related death be based on a history of exposure to high ambient temperature and the reasonable exclusion of other causes of hyperthermia. The diagnosis may be established from the circumstances surrounding the death, investigative reports concerning environmental temperature, and/or measured antemortem body temperature at the time of collapse.
In cases where the measured antemortem body temperature at the time of collapse was ≥105°F (≥40.6°C), the cause of death should be certified as heat stroke or hyperthermia. Deaths may also be certified as heat stroke or hyperthermia with lower body temperatures when cooling has been attempted prior to arrival at the hospital and/or when there is a clinical history of mental status changes and elevated liver and muscle enzymes.
In cases where the antemortem body temperature cannot be established but the environmental temperature at the time of collapse was high, an appropriate heat-related diagnosis should be listed as the cause of death or as a significant contributing condition. It is appropriate to certify a death as heat-related if the investigation provides compelling evidence of continuous exposure to a hot environment and fails to identify an independent cause of death. A significant number of these deaths will occur in persons having some preexisting disease known to be exacerbated by heat stress. These deaths can be certified as heat-related, with the disease being considered a significant contributing condition, or vice versa. The specific term used is less important than the fact that its use be consistent over time.
The diagnosis of heat-related death is based principally on investigative information; autopsy findings are nonspecific. In the epidemic situations encountered in Philadelphia, Milwaukee, and Chicago, the number of fatalities rapidly exceeded the autopsy capabilities of the medical examiners' offices involved. The committee recommends that the decision to autopsy should be based on the circumstances of the death, the age of the deceased, and the available resources.
The collection of blood, urine, and vitreous humor for toxicologic examination is highly desirable if the condition of the body allows it. When these specimens are collected and preserved, toxicologic analyses can be performed as resources become available. In cases of heat-related death occurring during a heat wave, toxicologic analyses will usually not affect the determination of the cause of death but may help identify risk factors and contributory conditions.
1. CDC. Heat-related mortality-Chicago, July 1995. MMWR
2. CDC. Heat-wave-related mortality-Milwaukee, Wisconsin, July 1995. MMWR
3. CDC. Heat-related deaths-Philadelphia and United States, 1993-1994. MMWR CDC Surveill Summ
4. Mirchandani HG, McDonald G, Hood IC, Fonseca C. Heat-related deaths in Philadelphia. Am J Forensic Med Pathol
5. City of Chicago. Final report: mayor's commission on extreme weather
conditions. Chicago: City of Chicago, Nov. 1995:2.
6. Semenza JC, Rubin CH, Falter KH, et al. Heat-related death during the July 1995 heat wave in Chicago. N Engl J Med
7. Tek D, Olshaker JS. Heat illness. Emerg Med Clin North Am
8. Clowes GHA Jr, O'Donnell TF Jr. Heat stroke. N Engl J Med
9. Malamud N, Haymaker W, Custer RP. Heat stroke: a clinicopathologic study of 125 fatal cases. Mil Surg
10. Jones TS, Liang AP, Kilbourne EM, et al. Morbidity and mortality associated with the July 1980 heat wave in St. Louis and Kansas City, MO. JAMA
11. Kellerman AL, Todd KH. Killing heat. N Engl J Med