Hypothermia-Related Mortality --- Montana, 1999--2004

Hypothermia, defined as a core body temperature of <95°F (35°C), occurs in persons exposed to excessive cold. Although hypothermia can be fatal, it also is preventable. Risk factors for death from hypothermia include advanced age, substance abuse, altered mental status, and increased contact with substances that promote heat loss, such as water (1). Montana has an intensely cold and long winter. In December, the average daily minimum temperature is approximately 18.0°F (-7.7°C) and can remain at that level until March. For the entire year in Montana, the average daily minimum temperature is 35.9°F (2.2°C) (2). During the period 1999--2004, Montana had the second highest (after Alaska) average annual hypothermia-related mortality rate (1.08 deaths per 100,000 population) in the United States, approximately five times greater than the U.S. rate overall. This report describes three examples of case reports of hypothermia-related deaths in Montana during 2005--2006, summarizes hypothermia-related mortality in the state during 1999--2004 (the most recent period for which annual data were available), and discusses hypothermia risk factors and prevention measures. Enhanced education and intervention strategies, particularly targeted to older adults, might reduce the number of deaths from hypothermia in Montana.

Case Reports

Case 1. In November 2005, a man aged 88 years left home to work in the fields. When he did not return for dinner, his wife notified a neighbor, who found the man pinned at the thighs between a flatbed trailer and livestock panels. The man was in pain and said he was cold; he had diminished level of consciousness. The ambient air temperature was 47.0°F (8.3°C) with 13-mph winds. The man was extricated by the neighbor and brought to the hospital. He had moderate muscle stiffness and was unable to respond to commands. His core body temperature was 84.7°F (29.3°C). The patient died 2 days later in the hospital. Primary cause of death was severe hypothermia; secondary causes were crush injuries to the thighs and multiorgan failure.

Case 2. In November 2005, a man aged 49 years left his automobile in a wooded area to go deer hunting just before sunset. He became lost in a forest and walked 6 miles across rugged and mountainous terrain. While he was missing, ambient temperatures ranged from 28.0°F to 40.0°F (-2.2°C to 4.4°C). A mixture of wet rain and snow fell during the night and most of the next day. Search crews tracked him and found him the next night, 30 hours after he had left his vehicle. The man was found dressed in thermal underwear, jeans, wool socks, sneakers, a cotton shirt, an oil-cloth coat, and a cowboy hat. All of his clothing was wet, and he smelled of wood smoke. He was carrying his rifle and a global positioning system unit. Trackers determined that the man had stumbled and fallen several times. When found, the man was unresponsive and cyanotic; his body was stiff, and he had no detectable respiration or pulse. After several hours of backcountry transport, the man was pronounced dead. The coroner certified death as fatal arrhythmia resulting from severe hypothermia.

Case 3. In February 2006, a woman aged 43 years attempted to drive home late at night down a little-traveled road. When she did not arrive home, her husband looked for her along the road but could not find her in the dark and assumed she had spent the night in town. Ambient air temperatures that night ranged between -10.0°F and -15.0°F (-23.3°C to -26.1°C). The woman was found the next morning by a rancher who noticed her car, which had gone off the road and down a steep embankment after she had apparently missed a sharp turn. She was found dead in her car. On autopsy, she had no significant traumatic injuries but a blood alcohol concentration of 0.15 g/dL, nearly twice the state legal limit of 0.08 g/dL for drivers. Cause of death was hypothermia.

Hypothermia-Related Mortality, 1999--2004

Data on hypothermia-related deaths in Montana were obtained from the Compressed Mortality File and accessed via CDC's Wonder database.* The International Classification of Diseases, Tenth Revision (ICD-10) was used to identify the external cause of mortality: exposure to excessive natural cold. Hypothermia deaths were identified by ICD-10 code X31 (3).

During 1999--2004, Montana reported 59 hypothermia-related deaths, ranging from seven deaths in 2002 and 2004 to 13 deaths in 2001 (Table). Thirty-one (53%) victims were aged >65 years, and 20 (34%) were aged 45--64 years. Because fewer than 20 hypothermia deaths were recorded in Montana each year, producing statistically unreliable annual hypothermia-related death rates, an aggregate crude rate was calculated by combining data for the entire period 1999--2004. Montana's 59 deaths during that period produced a crude rate for hypothermia-related mortality of 1.08 per 100,000 population, approximately five times greater than that of the United States as a whole (3,881 deaths, for a crude rate of 0.23 per 100,000 population) (Table).

Reported by: S Halvorson, MD, D Givens, MD, S Helgerson, MD, K Johnson, DVM, Montana Dept of Health. C Sanchez, MD, E Azziz-Baumgartner, MD, A Wolkin, MPH, D Batts, MD, M Belson, MD, C Rubin, DVM, M McGeehin, PhD, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; L Hausman, MPH, EIS Officer, CDC.

Editorial Note:

This report supports previous U.S. findings that persons aged >65 years and males are at greater risk for death by hypothermia (1,4). Older age might be a risk factor because of lower metabolic rate, which in turn might prevent maintaining a normal body temperature when indoor or outdoor temperatures fall below 64.4°F (18.0°F) (1). In addition, alcohol consumption is a risk factor because it triggers increased heat loss via vasodilation (5). Alcohol and drugs also can alter a person's mental status, impairing behavioral responses and increasing the risk for exposure to cold. Contact with cold water or other substances that promote heat loss also can cause hypothermia through conduction (the transfer of heat via contact with a cooler object) (5). Although only one person aged <15 years died from hypothermia in Montana during the study period, populations at risk for hypothermia also can include very young children and persons with comorbid medical conditions. These persons might have difficulty regulating their body temperature, thus increasing their risk for hypothermia (6).

Hypothermia is classified as mild, moderate, or severe, as determined by core body temperature (5). In severe cases of hypothermia, the brain is affected and victims are unable to think clearly or move well, which can further exacerbate their exposure. Warning signs of hypothermia in adults are shivering, exhaustion, confusion, fumbling hands, memory loss, slurred speech, and drowsiness (7).

During periods of excessively cold weather, persons can reduce their risk for hypothermia by taking the following precautions: 1) covering exposed skin and wearing a hat to prevent heat loss, 2) avoiding overexertion that might cause sweating and increased cardiac stress, 3) wearing loose-fitting layers of clothing that trap heat close to the body, 4) avoiding consumption of alcohol and other drugs that can impair judgment, and 5) staying dry by avoiding contact with cold substances that promote heat loss (8). In addition, persons living or traveling in cold environments can reduce their risk for hypothermia by preparing a winter storm plan, assembling a disaster supplies kit, being aware of storm warnings and the wind chill factor, leaving a travel itinerary with a friend or family member, carrying a cellular telephone, and avoiding travel during winter storms (9). Enhanced public health education and community intervention strategies might reduce the risk for hypothermia in persons at greatest risk.

References

1. CDC. Hypothermia-related deaths---United States, 2003--2004. MMWR 2005;54:173--5.
2. Western Regional Climate Center. Western U.S. climate historical summaries. Reno, NV: Western Regional Climate Center. Available at http://www.wrcc.dri.edu/climsum.html.
3. World Health Organization. International statistical classification of diseases and related health problems, tenth revision. Geneva, Switzerland: World Health Organization; 1992.
4. Weinberg AD. Hypothermia. Ann Emerg Med 1993;22:370--7.
5. McCullough L, Arora S. Diagnosis and treatment of hypothermia. Am Fam Physician 2004;70:2325--32.
6. CDC. Hypothermia-related deaths---United States, 1999--2002 and 2005. MMWR 2006;55:282--4.
7. CDC. Extreme cold: a prevention guide to promote your personal health and safety. Atlanta, GA: US Department of Health and Human Services, CDC; 2004. Available at http://www.bt.cdc.gov/disasters/winter/guide.asp.
8. Mayo Foundation for Medical Education and Research. Hypothermia: tools for healthier lives; 2005. Available at http://www.mayoclinic.com/health/hypothermia/ds00333/dsection=8.
9. American Red Cross. Talking about disaster: guide to standard messages. Are you ready for a winter storm? Washington, DC: American Red Cross, 1998; 147--57.

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Date last reviewed: 4/18/2007