Risk factors for recruit exertional heat illness by gender and training period.

INTRODUCTION: Exertional heat illness (EHI) is a recurrent problem for both male and female recruits during basic military training. A matched case control study investigated the effects of fitness and conditioning on EHI risk among Marine Corps recruits during 12 wk of basic training at Marine Corps Recruit Depot, Parris Island, SC. METHODS: Physical fitness and anthropometric measurements at entrance were acquired for 627 EHI cases that occurred during the period 1988-1996 and for 1802 controls drawn from the same training platoons. Conditional logistic regression was used to estimate EHI risk. RESULTS: Slower physical fitness test run times during processing week strongly predicted risk for subsequent EHI in both male and female recruits. A 9% increase in risk for EHI associated with body mass index (BMI = kg x m(-2); weight/height2) was found in male recruits, while BMI was not associated with risk among female recruits. BMI and initial run time were important predictors for EHI in early training, while in late training the initial BMI was no longer as important a risk factor and improvements in fitness reduced risk. CONCLUSION: Tables of estimated absolute risks categorized by BMI and VO2max are provided as a guide for identifying recruits who are at high risk for developing EHI during training.

Nontraumatic deaths during U.S. Armed Forces basic training, 1977-2001.

BACKGROUND: A Recruit Mortality Registry, linked to the Department of Defense Medical Mortality Registry, was created to provide comprehensive medical surveillance data for deaths occurring during enlisted basic military training. METHODS: Recruit deaths from 1977 through 2001 were identified and confirmed through redundant sources. Complete demographic, circumstantial, and medical information was sought for each case and recorded on an abstraction form. Mortality rates per 100,000 recruit-years were calculated by using recruit accession data from the Defense Manpower Data Center. RESULTS: There were 276 recruit deaths from 1977 through 2001 and age-specific recruit mortality rates were less than half of same-age U.S. civilian mortality rates. The majority (72%) of recruit deaths were classified as nontraumatic and 70% of these deaths (139 of 199) were related to exercise. Of the exercise-related deaths, 59 (42%) were cardiac deaths, and heat stress was a primary or contributory cause in at least 46 (33%). Infectious agents accounted for only 49 (25%) of the nontraumatic deaths. Nontraumatic death rates increased with age (rate ratio is 2.5 for 25+ v <25 years; p<0.001). The age- and gender-adjusted nontraumatic death rates were 2.6 times higher for African American than non-African American recruits (p<0.001). CONCLUSIONS: Although recruit mortality rates are lower than the same-age U.S. civilian population, preventive measures focused on reducing heat stress during exercise might be effective in decreasing the high proportion of exercise-related death. The availability of 25 years of comprehensive recruit mortality data will permit the ongoing evaluation of cause-of-death trends, effectiveness of preventive measures, and identification of emerging threats during basic military training.

Predictors of hospitalization in male Marine Corps recruits with exertional heat illness.

Exertional heat illness can have serious consequences and is a common cause of hospitalization during basic military training. The objective of this case-control study was to determine risk factors for hospitalization in male Marine Corps recruits who received medical care for heat illness during their basic military training course at Parris Island, South Carolina. Of 565 heat casualties, 61 (11%) were hospitalized (case subjects) and 504 were treated as outpatients (control subjects). Using univariate and multivariate analyses, demographic, clinical, and laboratory factors were assessed to determine predictors of hospitalization. Nineteen of the 24 analyzed variables were significantly associated with hospitalization. Three clinical variables (disorientation, rectal temperature, systolic blood pressure) and three laboratory variables (serum lactate dehydrogenase, potassium, and creatinine values) were highly predictive for hospitalization in recruits with exertional heat illness. A simple scoring system using these six variables predicted hospitalization with 87% sensitivity, 91% specificity, and a likelihood ratio of 9.7.

Nontraumatic exercise-related deaths in the U.S. military, 1996-1999.

We identified 215 exercise-related deaths in U.S. military personnel on active duty during 1996-1999. The most complete case information was for active duty Army personnel during 1998-1999, providing an exercise-related death rate of 4.3 per 100,000 person-years (41/963,000) and accounting for 6% of Army deaths (14 during physical fitness testing). The cause of death was confirmed by autopsy or clinical data for 85% of the cases. Arteriosclerotic coronary artery disease was the predominant cause of death for those 30 to 58 years of age. For age 17 to 34 years, 50% of deaths were attributable to preexisting heart disease (16% from coronary anomalies), 20% attributable to nontraumatic drowning, and 12% attributable to exertional heat illness, also a potential contributory factor in cardiac deaths. Most exercise-related deaths were related to running (60%), sports (14%), and swimming (13%). Improvements in health promotion, medical management, and stricter exclusion from inappropriate exercise (especially fitness test runs) could reduce these deaths.

Fluorescence measurements of the labile iron pool of sickle erythrocytes.

Sickle erythrocytes have increased ferritin and increased molecular iron on the inner membrane leaflet, and we postulated that cytosolic labile iron is also elevated. We used the fluorescent metallosensor, calcein, and a permeant Fe2+ chelator to estimate labile cytoslic Fe2+, and calcein plus an Fe3+ chelator to estimate total cytosolic labile iron (Fe2+ + Fe3+). We measured membrane nonheme iron by its reactivity with ferrozine. As estimated by calcein and Fe2+ chelator, the mean +/- SD labile Fe2+ concentration was significantly lower in hemoglobin (Hb) SS (n = 29) than hemoglobin AA (n = 17) erythrocytes (0.56 +/- 0.35 microM versus 1.25 +/- 0.65 microM; P <.001). In contrast, as estimated by calcein and Fe3+ chelator, total erythrocyte labile iron was similar in hemoglobin SS (n = 12) and hemoglobin AA (n = 10) participants (1.75 +/- 0.41 microM versus 2.14 +/- 0.93 microM; P =.2). Mean membrane nonheme iron levels were higher in hemoglobin SS cells than hemoglobin AA cells (0.0016 x 10-4 versus 0.0004 x 10-4 fmol/cell; P =.01), but much lower than the mean amounts of total labile iron (1.6-1.8 x 10-4 fmol/cell) or hemoglobin iron (18 000-19 000 x 10-4 fmol/cell). Both membrane iron and total labile iron were much less than the mean amount of iron potentially present in erythrocyte ferritin as calculated from results of other investigators (15 x 10-4 versus 34 x 10-4 fmol/cell in HbAA versus HbSS erythrocytes). We conclude that cytosolic labile iron is not elevated in hemoglobin SS erythrocytes and that elemental membrane iron is present in only trace amounts.