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Update: Cold Weather Injuries, Active and Reserve Components, U.S. Armed Forces, July 2014–June 2019

A U.S. Marine with Marine Rotational Force-Europe (MRF-E) 19.1 maintains a defensive security position during Exercise Winter Warrior in Haltdalen, Norway, Dec. 5, 2018. The three-week exercise tested the Marines' abilities to adapt to harsh weather conditions, move across long distances in the snow and push themselves to complete the mission despite austere situations. (U.S. Marine Corps photo by Cpl. Elijah Abernathy/Released) A U.S. Marine with Marine Rotational Force-Europe (MRF-E) 19.1 maintains a defensive security position during Exercise Winter Warrior in Haltdalen, Norway, Dec. 5, 2018. The three-week exercise tested the Marines' abilities to adapt to harsh weather conditions, move across long distances in the snow and push themselves to complete the mission despite austere situations. (U.S. Marine Corps photo by Cpl. Elijah Abernathy/Released)

Recommended Content:

Medical Surveillance Monthly Report

ABSTRACT

From July 2018 through June 2019, a total of 513 members of the active (n=446) and reserve (n=67) components had at least 1 medical encounter with a primary diagnosis of cold injury. The crude overall incidence rate of cold injury for all active component service members in 2018–2019 (36.5 per 100,000 person-years [p-yrs]) was slightly higher than the rate for the 2017–2018 cold season (35.8 per 100,000 p-yrs) and was the highest rate during the 5-year surveillance period. In 2018–2019, frostbite was the most common type of cold injury among active component service members in all 4 services. Among active component members during the 2014–2019 cold seasons, overall rates of cold injuries were generally highest among males, non-Hispanic black service members, the youngest (less than 20 years old), and those who were enlisted. As noted in prior MSMR updates, the rate of all cold injuries among active component Army members was higher in women than in men because of a much higher rate of frostbite among female soldiers. The number of cold injuries associated with overseas deployments during the 2018–2019 cold season (n=24) was the highest count during the 5-year surveillance period.

WHAT ARE THE NEW FINDINGS?    

For all active component service members, the rate of cold weather injuries in 2018–2019 was the highest of the last 5 seasons. Cold injury rates were much higher among members of the Marine Corps and Army. Cold injuries associated with deployment during 2018–2019 were much more numerous than any of the previous 4 years; frostbite accounted for most such injuries.

WHAT IS THE IMPACT ON READINESS AND FORCE HEALTH PROTECTION?

U.S. military forces will likely be deployed in cold, northern latitudes for peacekeeping and national security operations because of the opening of new shipping lanes in the Arctic Ocean. Such operations will require renewed emphasis on effective cold weather injury prevention strategies and adherence to the policies and procedures in place to protect service members against such injuries.

BACKGROUND

Cold weather injuries are of significant military concern because of their adverse impact on operations and the high financial costs of treatment and disability.1,2 In response, the U.S. Armed Forces have developed and improved training, doctrine, procedures, and protective equipment and clothing to counter the threat from cold environments.3–8 Although these measures are highly effective, cold injuries have continued to affect hundreds of service members each year because of exposure to cold and wet environments.9

The term cold weather injuries is used to describe injuries that have a central effect, such as hypothermia, as well as those that primarily affect the peripheries of the body, such as frostbite and immersion injuries. The human physiologic response to cold exposure is to retard heat loss and preserve core body temperature, but this response may not be sufficient to prevent hypothermia if heat loss is prolonged.9 Moreover, the response includes constriction of the peripheral (superficial) vascular system, which may result in non-freezing injuries or hasten the onset of actual freezing of tissues (frostbite).9

Hypothermia occurs when the core temperature of the body falls below 95°F.7 The most common mechanisms of accidental hypothermia are convective heat loss to cold air and conductive heat loss to water.10 Freezing temperatures are not required to produce hypothermia.10 In response to cold stress, peripheral blood vessels constrict and the hypothalamus stimulates heat production through shivering and elevated thyroid, adrenal, and catecholamine activity.10 The sympathetic nervous system mediates further vasoconstriction to minimize heat loss by reducing blood flow to the extremities, where the most cooling occurs.10 As the body’s basal metabolic rate decreases, core temperature falls, body functions slow down, and muscular and cerebral functions are impaired.10 Neurologic functioning begins declining even above a core body temperature of 95°F.11 Severe hypothermia can lead to pulmonary edema, reduced heart rate, coma, ventricular arrhythmias (including ventricular fibrillation), and asystole.10–12

Cold injuries affecting the body’s peripheries can be classified as freezing and non-freezing injuries.13 Freezing peripheral injury is defined as the damage sustained by tissues when exposed to temperatures below freezing.13 The tissue damage of frostbite is the result of both direct cold-induced cell death and the secondary effects of microvascular thrombosis and subsequent ischemia.14 Rapid freezing generally results in extra- and intracellular ice crystal formation.15 These crystals cause direct injury to the cell membrane that results in cellular dehydration, lipid derangement, electrolyte fluxes, membrane lysis, and cell death.14–16 An inflammatory process follows, resulting in tissue ischemia and additional cell death.15 The initial cellular damage and the ensuing inflammatory processes are worsened with thawing of the affected area.15,16 With rewarming, edema from melting ice crystals leads to epidermal blister formation and ischemia-reperfusion injury may be initiated 14–16; vasoconstriction and platelet aggregation caused by inflammatory mediators, prostaglandins, and thromboxanes exacerbate ischemia.17 The areas of the body most frequently affected by frostbite include the ears, nose, cheeks, chin, fingers, and toes.18,19 A substantial proportion of patients with peripheral frostbite experience permanent changes in their microcirculation and disruption of local neurological functions (e.g., reduced sensation in the affected area).19 Although most frostbite damage is minor, severe injury may lead to impaired functioning and ability to work because of cold hypersensitivity, chronic ulceration, vasospasm, localized osteoarthritis, and/or chronic pain.14,19

Non-freezing peripheral cold injury includes a spectrum of localized injuries to the soft tissues, nerves, and vasculature of distal extremities that result from prolonged exposure (12 to 48 hours) to wet, cold (generally 32 to 59°F) conditions; the injury process generally happens at a slower rate in warmer water.13,20 Although non-freezing peripheral cold injuries most often involve feet (immersion foot), any dependent body part can be affected by the condition, including the hands.21 Immersion foot generally presents as waterlogging of the feet, with the most marked effect occurring in the soles.17,20 The foot becomes hyperemic (increased blood flow), painful, and swollen with continuous exposure; progression to blistering, decreased blood flow, ulceration, and gangrene is gradual.17,20 Long-term complications of non-freezing cold injury such as immersion foot are similar to (e.g., hypersensitivity to cold, chronic pain) and as debilitating as (e.g., severe pain provoked by walking) those produced by frostbite.14,16,17,20

Factors that increase the risk of cold weather injuries include outdoor exposure, inadequate and/or wet clothing, cold water submersion, older age, exhaustion, dehydration, inadequate caloric intake, alcohol use, smoking (frostbite), previous cold injury (frostbite or immersion foot), chronic disease (e.g., peripheral vascular disease, diabetes), and medications that impair compensatory responses (e.g., oral antihyperglycemics, beta-blockers, general anesthetic agents).12–14,17–19 Situational factors that increase risk of immersion foot include immobility, wet socks, and constricting boots.17,22

Traditional measures to counter the dangers associated with cold environments include minimizing loss of body heat and protecting superficial tissues through means such as protective clothing, shelter, physical activity, and nutrition. However, military training or mission requirements in cold and wet weather may place service members in situations where they may be unable to be physically active, find warm shelter, or change wet or damp clothing.2–4

For the military, continuous surveillance of cold weather injuries is essential to inform steps to reduce their impact as well as to remind leaders of this predictable threat. Since 2004, the MSMR has published annual updates on the incidence of cold weather injuries that affected U.S. military members during the 5 most recent cold seasons.23 The content of this 2019 report addresses the occurrence of such injuries during the cold seasons from July 2014 through June 2019. The timing of the annual updates is intended to call attention to the recurring risks of such injuries as winter approaches in the Northern Hemisphere, where most members of the U.S. Armed Forces are assigned.

METHODS

The surveillance period was 1 July 2014 through 30 June 2019. The surveillance population included all individuals who served in the active or reserve component of the U.S. Armed Forces at any time during the surveillance period. For analysis purposes, “cold years” or “cold seasons” were defined as 1 July through 30 June intervals so that complete cold weather seasons could be represented in year-to-year summaries and comparisons.

Because cold weather injuries represent a threat to the health of individual service members and to military training and operations, the U.S. Armed Forces require expeditious reporting of these reportable medical events (RMEs) via one of the service-specific electronic reporting systems; these reports are routinely incorporated into the Defense Medical Surveillance System (DMSS). For this analysis, the DMSS and the Theater Medical Data Store (which maintains electronic records of medical encounters of deployed service members) were searched for records of RMEs and inpatient and outpatient care for the diagnoses of interest (frostbite, immersion injury, and hypothermia). A case was defined by the presence of an RME or of any qualifying International Classification of Diseases, 9th or 10th Revision (ICD-9 and ICD-10, respectively) code in the first diagnostic position of a record of a healthcare encounter (Table 1). The Department of Defense guidelines for RMEs require the reporting of cases of hypothermia, freezing peripheral injuries (i.e., frostbite), and non-freezing peripheral injuries (i.e., immersion injuries, chilblains).24 Cases of chilblains are not included in this report because the condition is common, infrequently diagnosed, usually mild in severity, and thought to have minimal medical, public health, or military impacts. Because of an update to the Disease Reporting System internet (DRSi) medical event reporting system in July 2017, the type of RMEs for cold injury (i.e., frostbite, immersion injury, hypothermia) could not be distinguished using RME records in DMSS data. Instead, information on the type of RME for cold injury between July 2017 and June 2019 were extracted from the DRSi and then combined with DMSS data.

To estimate the number of unique individuals who suffered a cold injury each cold season and to avoid counting followup healthcare encounters after single episodes of cold injury, only 1 cold injury per individual per cold season was included. A slightly different approach was taken for summaries of the incidence of the different types of cold injury diagnoses. In counting types of diagnoses, 1 of each type of cold injury per individual per cold season was included. For example, if an individual was diagnosed with immersion foot at one point during a cold season and then with frostbite later during the same cold season, each of those different types of injury would be counted in the tally of injuries. If a service member had multiple medical encounters for cold injuries on the same day, only 1 encounter was used for analysis (hospitalizations were prioritized over ambulatory visits, which were prioritized over RMEs).

Annual incidence rates of cold injuries among active component service members were calculated as incident cold injury diagnoses per 100,000 person-years (p-yrs) of service. Annual rates of cold injuries among reservists were calculated as cases per 100,000 persons using the total number of reserve component service members for each year of the surveillance period. Counts of persons were used as the denominator in these calculations because information on the start and end dates of active duty service periods of reserve component members was not available.

The numbers of cold injuries were summarized by the locations at which service members were treated for these injuries as identified by the Defense Medical Information System Identifier (DMIS ID) recorded in the medical records of the cold injuries. Because such injuries may be sustained during field training exercises, temporary duty, or other instances for which a service member may not be located at his/her usual duty station, DMIS ID was used as a proxy for the location where the cold injury occurred.

The new electronic health record for the Military Health System, MHS GENESIS, was implemented at several military treatment facilities during 2017. Medical data from sites using MHS GENESIS are not available in the DMSS. These sites include Naval Hospital Oak Harbor, Naval Hospital Bremerton, Air Force Medical Services Fairchild, and Madigan Army Medical Center. Therefore, medical encounter and person-time data for individuals seeking care at any of these facilities during 2017–30 June 2019 were not included in this analysis.

RESULTS

2018–2019 cold season

From July 2018 through June 2019, a total of 513 members of the active (n=446) and reserve (n=67) components had at least 1 medical encounter with a primary diagnosis of cold injury (Table 2). The Army contributed almost three-fifths (59.6%; n=266) of all cold injury diagnoses in the active component during the 2018–2019 cold season. Across the services during this period, the rate of cold injury diagnoses was highest among active component Marine Corps members (62.2 per 100,000 p-yrs). The 115 members of the Marine Corps diagnosed with a cold injury represented more than one-quarter (25.8%) of all affected active component service members. Navy service members (n=20) had the lowest service-specific rate of cold injuries (7.1 per 100,000 p-yrs) (Table 2, Figure 1).

This update for 2018–2019 represents the third time that annual rates of cold injuries for members of the reserve component were estimated. Army personnel (n=46) accounted for more than two-thirds (68.7%) of all reserve component service members (n=67) affected by cold injuries (Table 2). During this period, the rate of cold injury diagnoses was highest among reserve component Marine Corps members (30.8 per 100,000 persons) and lowest among reserve component Navy members (1.6 per 100,000 persons).

The overall rate of cold injuries for the reserve component and the rates for each of the services except the Air Force were lower than in the 2017–2018 season. Among reserve component members, the most pronounced decrease in service-specific rates of cold injuries between the 2017–2018 and 2018–2019 seasons was seen in the Marine Corps.

When all injuries were considered, not just the numbers of individuals affected, frostbite was the most common type of cold injury (n=241; 52.3% of all cold injuries) among active component service members in 2018–2019 (Tables 3a–3d). In the Air Force and Navy, 84.8% and 70.0%, respectively, of all cold injuries were frostbite, whereas the proportions in the Army (48.7%) and Marine Corps (44.8%) were much lower. Among active component Marine Corps members, the number and rate of frostbite injuries were the highest of the past 5 years. For all active component service members, the proportions of total cold weather injuries that were hypothermia and immersion injuries were 17.4% and 30.4%, respectively (data not shown). Among active component Navy members, the number and rate of immersion injuries in 2018–2019 were the lowest of the 5-year surveillance period (Table 3b). The rate of immersion injury cases in the Army was 41.4% higher than the rate for the 2017–2018 cold season (Table 3a).

Five cold seasons: July 2014–June 2019

The crude overall incidence rate of cold injury for all active component service members in 2018–2019 (36.5 per 100,000 p-yrs) was slightly higher than the rate for the 2017–2018 cold season (35.8 per 100,000 p-yrs) and was the highest rate during the 5-year period (Table 2, Figure 1). Throughout the surveillance period, the cold injury rates were consistently higher among active component members of the Army and the Marine Corps than among those in the Air Force and Navy (Figure 1). In 2018–2019, the service-specific incidence rate for active component Army members (60.2 per 100,000 p-yrs) was slightly lower than the 2017–2018 Army rate (62.4 per 100,000 p-yrs). For the Marine Corps, the active component rate for 2018–2019 was 28.1% higher than the rate for the previous season and 60.6% higher than the rate for the 2015–2016 season. As was true for the active component, service-specific annual rates of cold injuries among reserve component members were consistently higher among those in the Army and Marine Corps than among those in the Air Force or Navy (Figure 2). The most pronounced increase (143.8%) in rates was seen among reserve component Marine Corps members between the 2015–2016 and 2017–2018 seasons.

During the 5-year surveillance period, the rates of cold injuries among members of the active components of the Navy, Air Force, and Marine Corps were higher among men than women. Among active component Army members, the overall rate among women (55.7 per 100,000 p-yrs) was 7.7% higher than the rate among men (51.7 per 100,000 p-yrs). In all of the services during 2014–2019, women had lower rates of immersion injury and hypothermia than did males but higher rates of frostbite (except in the Navy and Air Force) (Tables 3a–3d). For active component service members in all 4 services combined, the overall rate of cold injury was 31.4% higher among males (33.6 per 100,000 p-yrs) than among females (25.6 per 100,000 p-yrs) (data not shown).

In all of the services, overall rates of cold injuries were higher among non-Hispanic black service members than among those of the other race/ethnicity groups. In particular, within the Marine Corps and Army and for all services combined, rates of cold injuries were more than twice as high among non-Hispanic black service members than among either non-Hispanic white service members or those in the “other/unknown” race/ethnicity group (Tables 3a–3d). The major underlying factor in these differences is that the rate of frostbite among non-Hispanic black members from all services combined was more than 3 times that of the other race/ethnicity groups, with the biggest differences apparent in the Marine Corps (more than 5 times) and the Army (more than 2 times) (data not shown). Additionally, across the active components of all services during 2014–2019, non-Hispanic black service members had incidence rates of cold injuries greater than the rates of other race/ethnicity groups in nearly every military occupational category (data not shown).

Across the services, rates of cold injuries were generally highest among the youngest service members (less than 20 years old) and tended to decrease with increasing age (Tables 3a–3d). Enlisted members of all 4 services had higher rates than officers. In the Army, Navy, and Air Force, rates of all cold injuries combined were highest among service members in combat-specific (infantry/artillery/combat engineering/armor) and motor transport occupations (Tables 3a–3c).

During the 5-year surveillance period, the 2,330 service members who were affected by any cold injury included 2,009 (86.2%) from the active component and 321 (13.8%) from the reserve component. Of all affected reserve component members, 67.3% (n=216) were members of the Army (Table 2). Overall, soldiers accounted for slightly more than three-fifths (60.3%) of all cold injuries affecting active and reserve component service members (Table 2, Figure 3).

Of all active component service members who were diagnosed with a cold injury (n=2,009), 190 (9.5% of the total) were affected during basic training. The Army (n=72) and Marine Corps (n=109) accounted for 95.3% of all basic trainees affected by cold injuries (data not shown). Additionally, during the surveillance period, 71 service members who were diagnosed with cold injuries (3.5% of the total) were hospitalized, and the vast majority (90.1%) of the hospitalized cases were members of either the Army (n=41) or Marine Corps (n=23) (data not shown).

Cold injuries during deployments

During the 5-year surveillance period, a total of 76 cold injuries were diagnosed and treated in service members deployed outside of the U.S. (data not shown). Of these, 32 (42.1%) were frostbite, 35 (46.1%) were immersion injuries, and 9 (11.8%) were hypothermia. Of these 76 cold injuries, slightly less than one-third (31.6%) occurred in the most recent cold season. There were 24 cold injuries during the 2018–2019 cold season but only 13 during 2014–2015, 11 each during 2015–2016 and 2016–2017, and 17 during 2017–2018 (data not shown). Frostbite accounted for more than half (n=13; 54.2%) of the cold weather injuries diagnosed and treated in service members deployed outside of the U.S. during the 2018–2019 cold season. The vast majority of these frostbite cases were male (84.6%) and almost half (47.2%) were 24 years old or younger (data not shown). Army members accounted for more than two-fifths (46.2%) of the frostbite cases diagnosed among service members deployed outside of the U.S. Afghanistan was recorded as the location of diagnosis for 4 of these frostbite cases; information on the locations where the diagnoses were made was unavailable for 7 of these 13 frostbite cases (data not shown).

Cold injuries by location

During the 5-year surveillance period, 21 military locations had at least 25 incident cold injuries among active and reserve component service members (Figure 4). Among these locations, those with the highest 5-year counts of incident injuries were Fort Wainwright, AK (n=152); Army Health Clinic Vilseck, Germany (n=141); Marine Corps Recruit Depot Parris Island/Beaufort, SC (n=97); Naval Medical Center San Diego, CA (n=75); Fort Drum, NY (n=74); and Fort Campbell, KY (n=73) (data not shown). During the 2018–2019 cold season, the numbers of incident cases of cold injuries were higher than the counts for the previous 2017–2018 cold season at 10 of the 21 locations (data not shown). The most noteworthy increases were observed at the Marine Corps’ Camp Pendleton and the Army’s Fort Riley and Fort Sill, where there were 28, 26, and 16 total cases diagnosed at each location in 2018–2019, respectively, compared to just 13, 11, and 5, respectively, the year before (data not shown). Figure 4 shows the numbers of cold injuries during 2018–2019 and the median numbers of cases for the previous 4 years for those locations that had at least 25 cases during the surveillance period. For 9 of the 21 installations, the numbers of cases in 2018–2019 were equal to or less than the median counts for the previous 4 years.

EDITORIAL COMMENT

Between the 2017–2018 and 2018–2019 cold seasons, there was a slight increase in the crude overall incidence rate of cold injuries among U.S. active component service members; the overall rate among reserve component members decreased slightly during this period. For active component service members in the Marine Corps, the rate of all cold injuries in 2018–2019 was the highest since the 2014–2015 season.

In 2018–2019, frostbite was the most common type of cold injury among active component service members. Factors associated with increased risk of cold injury in previous years were again noted during the most recent cold season. Compared to their respective counterparts, males, non-Hispanic black service members, the youngest (less than 20 years old), and those who were enlisted had higher overall rates of cold injuries. Increased rates of cold injuries affected nearly all enlisted and officer occupations among non-Hispanic black service members. Of note, rates of frostbite were markedly higher among non-Hispanic blacks compared to non-Hispanic whites and those in the other/unknown race/ethnicity group. These differences have been noted in prior MSMR updates, and the results of several studies suggest that other factors (e.g., physiologic differences and/or previous cold weather experience) are possible explanations for increased susceptibility.9,14,25–27 The number of cold injuries associated with deployment during 2018–2019 was more than the number in any other year during the surveillance period; frostbite accounted for the majority of the cold weather injuries in service members deployed outside of the U.S during the 2018–2019 cold season.

The opening of sea lanes in the Arctic Ocean increases the likelihood that U.S. military forces will be deployed in the cold, northern latitudes for peacekeeping and national security operations.28–31This shift will require renewed emphasis on effective cold weather injury prevention strategies and increased focus on adherence to the policies and procedures in place to protect service members against such injuries. It should be noted that this analysis of cold injuries was unable to distinguish between injuries sustained during official military duties (training or operations) and injuries associated with personal activities not related to official duties. RMEs for non-freezing peripheral injuries were excluded if “chilblains” was listed in the case comments; however, there may have been some RMEs for chilblains that were misclassified as immersion injury if chilblains was not listed in the case comments. To provide for all circumstances that pose the threat of cold weather injury, service members should know well the signs of cold injury and how to protect themselves against such injuries whether they are training, operating, fighting, or recreating under wet and freezing conditions.

The most current cold injury prevention materials are available at https://phc.amedd.army.mil/topics/discond/cip/Pages/Cold-Weather-Casualties-and-Injuries.aspx.

REFERENCES

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2. Paton BC. Cold, casualties, and conquests: the effects of cold on warfare. In: Pandolf KB, Burr RE, eds. Medical aspects of harsh environments, Volume 1. Falls Church, VA: Office of the Surgeon General; 2001:313–349.

3. Pozos RS (ed.). Section II: cold environments. In: Pandolf KB, Burr RE, eds. Medical aspects of harsh environments, Volume 1. Falls Church, VA: Office of the Surgeon General;2001:311–566.

4. DeGroot DW, Castellani JW, Williams JO, Amoroso PJ. Epidemiology of U.S. Army cold weather injuries, 1980–1999. Aviat Space Environ Med. 2003;74(5):564–570.

5. Headquarters, Department of the Army. Technical Bulletin Medical 508. Prevention and Management of Cold-Weather Injuries. 1 April 2005.

6. Headquarters, Department of the Army, Training and Doctrine Command. TRADOC Regulation 350-29. Prevention of Heat and Cold Casualties. 18 July 2016.

7. Headquarters, Department of the Army, Training and Doctrine Command. TRADOC Regulation 350-6. Enlisted Initial Entry Training Policies and Administration. 9 August 2019.

8. Castellani JW, O’Brien C, Baker-Fulco C, Sawka MN, Young AJ. Sustaining health and performance in cold weather operations. Technical Note No. TN/02-2. Natick, MA: U.S. Army Research Institute of Environmental Medicine; October 2001.

9. Armed Forces Health Surveillance Branch. Update: Cold weather injuries, active and reserve component, U.S. Armed Forces, July 2013–June 2018. MSMR. 2018;25(11):10–17.

10. Jolly BT, Ghezzi KT. Accidental hypothermia. Emerg Med Clin North Am. 1992;10(2):311–327.

11. Rischall ML, Rowland-Fisher A. Evidence-based management of accidental hypothermia in the emergency department. Emerg Med Pract. 2016;18(1):1–18. 

12. Biem J, Koehncke N, Classen D, Dosman J. Out of the cold: management of hypothermia and frostbite. CMAJ. 2003;168(3):305–311.

13. Imray CH, Oakley EH. Cold still kills: cold-related illnesses in military practice freezing and non-freezing cold injury. J R Army Med Corps. 2005;151(4):218–222.

14. Handford C, Thomas O, Imray CHE. Frostbite. Emerg Med Clin North Am. 2017;35(2):281–299.

15. Murphy JV, Banwell PE, Roberts AH, McGrouther DA. Frostbite: pathogenesis and treatment. J Trauma. 2000;48(1):171–178.

16. Petrone P, Kuncir EJ, Asensio JA. Surgical management and strategies in the treatment of hypothermia and cold injury. Emerg Med Clin North Am. 2003;21(4):1165–1178.

17. Imray C, Grieve A, Dhillon S, Caudwell Xtreme Everest Research Group. Cold damage to the extremities: frostbite and non-freezing cold injuries. Postgrad Med J. 2009;85(1007):481–488.

18. Harirchi I, Arvin A, Vash JH, Zafarmand V. Frostbite: incidence and predisposing factors in mountaineers. Br J Sports Med. 2005;39(12):898–901.

19. Ervasti O, Hassi J, Rintamaki H, et al. Sequelae of moderate finger frostbite as assessed by subjective sensations, clinical signs, and thermophysiological responses. Int J Circumpolar Health. 2000;59(2):137–145.

20. Hall A, Sexton J, Lynch B, et al. Frostbite and immersion foot care. Mil Med. 2018;183(suppl 2):168–171.

21. McMahon JA, Howe A. Cold weather issues in sideline and event management. Curr Sports Med Rep. 2012;11(3):135–141.

22. Centers for Disease Control and Prevention. Natural disasters and severe weather: trench foot or immersion foot. https://www.cdc.gov/disasters/trenchfoot.html. Accessed 7 October 2019.

23. Army Medical Surveillance Activity. Cold injuries, active duty, U.S. Armed Forces, July 1999–June 2004. MSMR. 2004;10(5):2–10.

24. Armed Forces Health Surveillance Branch. Armed Forces Reportable Events Guidelines an-Case Definitions, 2017. https://health.mil/Reference-Center/Publications/2017/07/17/Armed-Forces-Reportable-Medical-Events-Guidelines.

25. Burgess JE, Macfarlane F. Retrospective analysis of the ethnic origins of male British Army soldiers with peripheral cold weather injury. J R Army Med Corps. 2009;155(1):11–15.

26. Maley MJ, Eglin CM, House JR, Tipton MJ. The effect of ethnicity on the vascular responses to cold exposure of the extremities. Eur J Appl Physiol. 2014;114(11):2369–2379.

27. Kuht JA, Woods D, Hollis S. Case series of non-freezing cold injury: epidemiology and risk factors. J R Army Med Corps. 2018; pii: jramc-2018-000992.

28. Goldenberg S. Pentagon: global warming will change how US military trains and goes to war. Guardian. 13 October 2014. https://www.theguardian.com/environment/2014/oct/13/pentagon-global-warming-will-change-how-us-military-trains-and-goes-to-war. Accessed 16 October 2019.

29. Nindl BC, Billing DC, Drain JR, et al. Perspectives on resilience for military readiness and preparedness: report of an international military physiology roundtable. J Sci Med Sport. 2018;21(11):1116–1124.

30. Cooper H. Military drills in arctic aim to counter Russia, but the first mission is to battle the cold. New York Times. 12 April 2019. https://www.nytimes.com/2019/04/12/world/europe/global-warmingrussia-arctic-usa.html. Accessed 16 October 2019.

31. Office of the Under Secretary of Defense for Policy. Report to Congress: Department of Defense Arctic Strategy. https://media.defense.gov/2019/Jun/06/2002141657/-1/-1/1/2019-DOD-ARCTICSTRATEGY.PDF. Published June 2019. Accessed 31 October 2019

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A U.S. naval officer listens through his stethoscope to hear his patient’s lungs at Camp Schwab in Okinawa, Japan in 2018. (Photo courtesy of U.S. Marine Corps) photo by Lance Cpl. Cameron Parks)

Among service members deployed during 2018, injury/poisoning, musculoskeletal diseases, and signs/symptoms accounted for more than half of the total healthcare burden while deployed. Compared to the distribution of major burden of disease categories documented in garrison, a relatively greater proportion of in-theater medical encounters due to respiratory infections, skin diseases, infectious/parasitic diseases, and digestive diseases was documented.

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Medical Surveillance Monthly Report

Heat Illness

Infographic
4/1/2019
Heat Illness

This report summarizes reportable medical events of heat illness as well as heat illness-related hospitalizations and ambulatory visits among active component service members during 2018 and compares them to the previous 4 years. Episodes of heat stroke and heat exhaustion are summarized separately.

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Health Readiness | Armed Forces Health Surveillance Branch | Epidemiology and Analysis | Medical Surveillance Monthly Report | Public Health

Exertional Rhabdomyolysis

Infographic
4/1/2019
Exertional Rhabdomyolysis

Each year, the MSMR summarizes the numbers, rates, trends, risk factors, and locations of occurrences of exertional heat injuries, including exertional rhabdomyolysis. This report includes the data for 2014–2018.

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Health Readiness | Armed Forces Health Surveillance Branch | Epidemiology and Analysis | Medical Surveillance Monthly Report | Public Health

Exertional Hyponatremia

Infographic
4/1/2019
Exertional Hyponatremia

Each year, the MSMR summarizes the numbers, rates, trends, risk factors, and locations of occurrences of exertional heat injuries, including exertional rhabdomyolysis. This report includes the data for 2014–2018.

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Health Readiness | Armed Forces Health Surveillance Branch | Epidemiology and Analysis | Medical Surveillance Monthly Report | Public Health

Lyme Disease

Infographic
4/1/2019
Lyme Disease

Each year, the MSMR summarizes the numbers, rates, trends, risk factors, and locations of occurrences of exertional heat injuries, including exertional rhabdomyolysis. This report includes the data for 2014–2018.

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Health Readiness | Armed Forces Health Surveillance Branch | Epidemiology and Analysis | Medical Surveillance Monthly Report | Public Health

Update: Exertional Rhabdomyolysis, Active Component, U.S. Armed Forces, 2014–2018

Article
4/1/2019
U.S. Marines sprint uphill during a field training exercise at Marine Corps Air Station Miramar, California. to maintain contact with an aviation combat element, teaching and sustaining their proficiency in setting up and maintaining communication equipment.  (Photo Courtesy: U.S. Marine Corps)

Among active component service members in 2018, there were 545 incident diagnoses of rhabdomyolysis likely due to exertional rhabdomyolysis, for an unadjusted incidence rate of 42.0 cases per 100,000 person-years. Subgroup-specific rates in 2018 were highest among males, those less than 20 years old, Asian/Pacific Islander service members, Marine Corps and Army members, and those in combat-specific or “other/unknown” occupations. During 2014–2018, crude rates of exertional rhabdomyolysis increased steadily from 2014 through 2016 after which rates declined slightly in 2017 before increasing again in 2018. Compared to service members in other race/ethnicity groups, the overall rate of exertional rhabdomyolysis was highest among non-Hispanic blacks in every year except 2018. Overall and annual rates were highest among Marine Corps members, intermediate among those in the Army, and lowest among those in the Air Force and Navy. Most cases of exertional rhabdomyolysis were diagnosed at installations that support basic combat/recruit training or major ground combat units of the Army or the Marine Corps. Medical care providers should consider exertional rhabdomyolysis in the differential diagnosis when service members (particularly recruits) present with muscular pain or swelling, limited range of motion, or the excretion of dark urine (possibly due to myoglobinuria) after strenuous physical activity, particularly in hot, humid weather.

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Medical Surveillance Monthly Report

Update: Heat Illness, Active Component, U.S. Armed Forces, 2018

Article
4/1/2019
Drink water the day before and during physical activity or if heat is going to become a factor. (Photo Courtesy: U.S. Air Force)

In 2018, there were 578 incident diagnoses of heat stroke and 2,214 incident diagnoses of heat exhaustion among active component service members. The overall crude incidence rates of heat stroke and heat exhaustion diagnoses were 0.45 cases and 1.71 cases per 1,000 person-years, respectively. In 2018, subgroup-specific rates of incident heat stroke diagnoses were highest among males and service members less than 20 years old, Asian/Pacific Islanders, Marine Corps and Army members, recruit trainees, and those in combat-specific occupations. Subgroup-specific incidence rates of heat exhaustion diagnoses in 2018 were notably higher among service members less than 20 years old, Asian/Pacific Islanders, Army and Marine Corps members, recruit trainees, and service members in combat-specific occupations. During 2014–2018, a total of 325 heat illnesses were documented among service members in Iraq and Afghanistan; 8.6% (n=28) were diagnosed as heat stroke. Commanders, small unit leaders, training cadre, and supporting medical personnel must ensure that the military members whom they supervise and support are informed about the risks, preventive countermeasures, early signs and symptoms, and first-responder actions related to heat illnesses.

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Medical Surveillance Monthly Report

Modeling Lyme Disease Host Animal Habitat Suitability, West Point, New York

Article
4/1/2019
A deer basks in the morning sun at Joint Base San Antonio-Fort Sam Houston, Texas.  (Photo Courtesy: U.S. Air Force)

As the most frequently reported vector-borne disease among active component U.S. service members, with an incidence rate of 16 cases per 100,000 person-years in 2011, Lyme disease poses both a challenge to healthcare providers in the Military Health System and a threat to military readiness. Spread through the bite of an infected blacklegged tick, infection with the bacterial cause of Lyme disease can have lasting effects that may lead to medical discharge from the military. The U.S. Military Academy at West Point is situated in a highly endemic area in New York State. To identify probable areas where West Point cadets as well as active duty service members stationed at West Point and their families might contract Lyme disease, this study used Geographic Information System mapping methods and remote sensing data to replicate an established spatial model to identify the likely habitat of a key host animal—the white-tailed deer.

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Medical Surveillance Monthly Report

Incidence, Timing, and Seasonal Patterns of Heat Illnesses During U.S. Army Basic Combat Training, 2014–2018

Article
4/1/2019
U.S. Marines participate in morning physical training during a field exercise at Marine Corps Base Camp Pendleton, California. (Photo Courtesy: U.S. Marine Corps)

Risk factors for heat illnesses (HIs) among new soldiers include exercise intensity, environmental conditions at the time of exercise, a high body mass index, and conducting initial entry training during hot and humid weather when recruits are not yet acclimated to physical exertion in heat. This study used data from the Defense Health Agency’s–Weather-Related Injury Repository to calculate rates and to describe the incidence, timing, and geographic distribution of HIs among soldiers during U.S. Army basic combat training (BCT). From 2014 through 2018, HI events occurred in 1,210 trainees during BCT, resulting in an overall rate of 3.6 per 10,000 BCT person-weeks (p-wks) (95% CI: 3.4–3.8). HI rates (cases per 10,000 BCT p-wks) varied among the 4 Army BCT sites: Fort Benning, GA (6.8); Fort Jackson, SC (4.4); Fort Sill, OK (1.8); and Fort Leonard Wood, MO (1.7). Although the highest rates ofHIs occurred at Fort Benning, recruits in all geographic areas were at risk. The highest rates of HI occurred during the peak training months of June through September, and over half of all HI cases affected soldiers during the first 3 weeks of BCT. Prevention of HI among BCT soldiers requires relevant training of both recruits and cadre as well as the implementation of effective preventive measures.

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Medical Surveillance Monthly Report

Update: Exertional Hyponatremia, Active Component, U.S. Armed Forces, 2003–2018

Article
4/1/2019
Drink water the day before and during physical activity or if heat is going to become a factor. (Photo Courtesy: U.S. Air Force)

From 2003 through 2018, there were 1,579 incident diagnoses of exertional hyponatremia among active component service members, for a crude overall incidence rate of 7.2 cases per 100,000 person-years (p-yrs). Compared to their respective counterparts, females, those less than 20 years old, and recruit trainees had higher overall incidence rates of exertional hyponatremia diagnoses. The overall incidence rate during the 16-year period was highest in the Marine Corps, intermediate in the Army and Air Force, and lowest in the Navy. Overall rates during the surveillance period were highest among Asian/Pacific Islander and non-Hispanic white service members and lowest among non-Hispanic black service members. Between 2003 and 2018, crude annual incidence rates of exertional hyponatremia peaked in 2010 (12.7 per 100,000 p-yrs) and then decreased to 5.3 cases per 100,000 p-yrs in 2013 before increasing in 2014 and 2015. The crude annual rate in 2018 (6.3 per 100,000 p-yrs) represented a decrease of 26.5% from 2015. Service members and their supervisors must be knowledgeable of the dangers of excessive water consumption and the prescribed limits for water intake during prolonged physical activity (e.g., field training exercises, personal fitness training, and recreational activities) in hot, humid weather.

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Medical Surveillance Monthly Report
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