Hypothermia is defined as an unintentional lowering of the core body temperature to less than or equal to 95 F (less than or equal to 35 C) (1). It is a medical emergency with a high fatality rate (2). In the United States, hypothermia-related deaths can occur anywhere, including in states with milder climates (e.g., Georgia and North Carolina) where weather systems can cause rapid changes in temperature. However, the highest hypothermia-related death rates in the United States occur in northern states, where winter is characterized by moderate to severe cold temperatures (e.g., Alaska and Montana), and western states, where profound declines in nighttime temperatures may occur at high elevations (e.g., New Mexico). From October 1998 through April 1999, 16 deaths attributed to hypothermia (International Classification of Diseases, Ninth Revision [ICD-9], codes E901.0, E901.8, and E901.9; excludes man-made cold [E901.1]*) were reported to the Alaska State Medical Examiner. This report describes selected cases of hypothermia-related deaths in Alaska during October 1998-April 1999; compares age-, sex-, and race-specific rates in Alaska and the rest of the United States during 1979-1996; and summarizes trends for hypothermia-related deaths in the United States during 1979-1996.

Case 1. In February 1999, a 36-year-old man with a history of binge drinking was found dead between parked cars in the parking area of the local airport. He was last seen alive 18 hours earlier in an extremely intoxicated condition. External examination indicated no evidence of injury or violence except for superficial abrasions on the hands consistent with scraping around in the ice and snow at temperatures of -20 F to -25 F (-29 C to -32 C). The man's postmortem blood alcohol level was 100 mg/dL (the legal blood alcohol limit in Alaska is 100 mg/dL), and his urine alcohol level was 272 mg/dL. An autopsy was not conducted.

Case 2. In January 1999, a 36-year-old man from a northern Alaska village was reported missing after he did not return from a hunting trip. Weather conditions were clear and calm with a temperature of approximately -15 F (-26 C) when he left his village; however, late in the afternoon, 40 mph winds lowered chill factors to -80 F (-62 C), and visibility on the tundra decreased to less than 200 yards. The man was discovered frozen 6 days later in a small freshly dug snow cave adjacent to his disabled snowmobile. He was wearing a heavy down jacket, beaver hat, ski pants, and heavy felt-lined boots over his usual clothing. No alcoholic beverages were present among his effects. External examination indicated no substantial injuries and an autopsy was not conducted. 

Case 3. In March 1999, a 36-year-old man was found 300 yards from his village residence in rural Alaska approximately 7 hours after having last been seen alive. The body was clad only in a pair of briefs and a shirt. The man suffered from a seizure disorder, and in his postictal state would frequently lose awareness of his surroundings and walk around or outside his residence. He had been taking valproic acid for his condition. Postmortem levels of valproic acid indicated a blood concentration of 53.5 mg/mL (therapeutic range: 50.0-100.0 mg/mL). The unbound valproic acid concentration was 19.6 mg/mL (therapeutic range: 6.0 to 20.0 mg/mL). A blood test was negative for alcohol. Autopsy indicated no evidence of a natural disease process or of substantial trauma.

Of the 16 persons in Alaska whose deaths were attributed to hypothermia, 12 were men. The median age of decedents was 35 years (range: 15-75 years). During 1979-1996, the age-adjusted rate for hypothermia-related deaths in Alaska was 10 times higher than in the rest of the United States (3.0 per 100,000 population versus 0.3). Hypothermia-related deaths also were more likely to occur among men (rate ratio: 2.4 versus 2.0), persons aged less than 65 years (rate ratio: 0.3 versus 0.2), and non-whites and non-blacks** (rate ratio: 11.7 versus 2.0) in Alaska than elsewhere in the United States.

During 1979-1996, hypothermia-related death rates in the United States decreased significantly (p=0.014). In addition, rates decreased among all age and sex groups (Figure 1). Stratification by race indicated that the recent downward trend in hypothermia is strongest among black males aged greater than or equal to 65 years, a population that has one of the highest hypothermia-related death rates in the United States (1979-1996 rate: 6.7 per 100,000 population).

Reported by: MT Propst, MD, Anchorage; JP Middaugh, MD, State Epidemiologist, Div of Public Health, Alaska Dept of Health. Health Studies Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; and an EIS Officer, CDC.

Editorial Note:

The findings in this report indicate that hypothermia-related deaths in the United States have decreased significantly. Possible reasons for the decrease include changes in reporting, improved prevention measures, and/or more moderate winters. Increases in winter temperatures will result in fewer winter-related deaths (3).

Infants, the elderly, persons who are homeless or mentally ill, and persons with serious medical conditions are particularly at risk for hypothermia (4), especially if they use drugs that can induce vasodilatation and suppress the shivering response (e.g., sedatives, anxiolytics, phenothiazines, and tricyclic antidepressants) (5). Men take more risks than women and are more likely to remain outdoors for long periods (i.e., more men are homeless, hikers, and hunters) (4). Race-specific differences may reflect variations in socioeconomic determinants such as access to protective clothing, shelter, or medical care (6).

In all three cases in this report, staying outdoors was a major contributing risk factor for hypothermia. Traveling during extremely cold periods, especially when conditions produce high winds, requires careful planning, awareness of travel advisories, and knowledge of survival techniques should a person become stranded (4). Specific preventive measures include wearing adequate clothing (particularly headgear), maintaining fluid and caloric intake, avoiding fatigue, refraining from alcohol consumption, ensuring availability of emergency shelter, and avoiding heavy exertion (4).

Hypothermia can occur when even moderately low ambient temperatures (e.g., 60 F [15.5 C]) overcome a person's ability to conserve heat (2). The onset of hypothermia is often insidious, with early manifestations of exposure including shivering, numbness, fatigue, poor coordination, slurred speech, impaired mentation, blueness or puffiness of the skin, and irrationality (6). Early recognition and immediate care can improve the prognosis (7). Even if a person appears dead, cardiopulmonary resuscitation should be provided and continued while the person is being warmed, until the person responds, or medical aid becomes available. 

In 1997, Mississippi, Missouri, New Mexico, and Wisconsin established surveillance systems for hypothermia (8). Public education and outreach programs targeting high-risk populations are essential to reduce the risk for hypothermia-related death.

References

1. Kilbourne EM. Cold environments. In: Noji EK, ed. The public health consequences of disasters. New York: Oxford University Press, 1997:270-86.
2. Hector MG. Treatment of accidental hypothermia. Am Fam Physician 1992;45:785-92.
3. McMicheal AJ, Haines A, Slooff R, Kovats S, eds. Climate change and human health. Geneva, Switzerland: World Health Organization, 1996.
4. CDC. Extreme cold: a prevention guide to promote your personal health and safety. Atlanta, Georgia: US Department of Health and Human Services, CDC, 1996.
5. CDC. Hypothermia-related deaths--Virginia, November 1996-April 1997. MMWR 1997;46:1157-9.
6. CDC. Hypothermia--United States. MMWR 1983;32:46-8.
7. Danz DF, Pozos RS. Accidental hypothermia. N Engl J Med 1994;331:1756-60.
8. CDC. Monitoring environmental disease--United States, 1997. MMWR 1998;47:522-5.

* These data were obtained from the compressed mortality file (CMF), maintained by CDC's National Center for Health Statistics, and have been prepared according to the external cause-of-death codes from the ICD-9. The CMF contains information from death certificates filed in the 50 states and the District of Columbia.

** Data on race in the CMF were collected only for whites, blacks, and other races.

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