Predictors of Hospitalization in Male Marine Corps Recruits with Exertional Heat Illness

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1 MILITARY MEDICINE, 169, 3:169, 2004 Predictors of Hospitliztion in Mle Mrine Corps Recruits with Exertionl Het Illness Gurntor: COL John W. Grdner, MC FS USA Contributors: Shilp Hkre, DrPH; COL John W. Grdner, MC FS USA; COL John A. Krk, MC USA (Ret.); C. Bruce Wenger, MD PhD Exertionl het illness cn hve serious consequences nd is common cuse of hospitliztion during bsic militry trining. The objective of this cse-control study ws to determine risk fctors for hospitliztion in mle Mrine Corps recruits who received medicl cre for het illness during their bsic militry trining course t Prris Islnd, South Crolin. Of 565 het csulties, 61 (11%) were hospitlized (cse subjects) nd 504 were treted s outptients (control subjects). Using univrite nd multivrite nlyses, demogrphic, clinicl, nd lbortory fctors were ssessed to determine predictors of hospitliztion. Nineteen of the 24 nlyzed vribles were significntly ssocited with hospitliztion. Three clinicl vribles (disorienttion, rectl temperture, systolic blood pressure) nd three lbortory vribles (serum lctte dehydrogense, potssium, nd cretinine vlues) were highly predictive for hospitliztion in recruits with exertionl het illness. A simple scoring system using these six vribles predicted hospitliztion with 87% sensitivity, 91% specificity, nd likelihood rtio of 9.7. Introduction xertionl het illness (EHI) comprises brod spectrum of E syndromes rnging from exertionl het crmps, het exhustion, nd het injury to life-thretening rhbdomyolysis nd hetstroke. 1,2 Its onset is usully sudden nd cn be ftl under conditions of indequte hydrtion, sustined exercise, nd delyed medicl cre. 3 EHI occurs in the context of genertion of body het nd metbolic stresses of exercise nd thermoregultion, nd it is common problem with exertion in wrm nd humid environments. EHI csulties re generlly young nd physiclly ctive individuls, such s militry service personnel, mrthon runners, nd hevy lborers (e.g., miners nd industril workers). 2 7 The complex of exercise, retined het, thermoregultion, sweting, nd metbolic nd crdiovsculr responses my led to dehydrtion, electrolyte imblnce, dmge to body tissues, nd clinicl syndromes tht ffect multiple orgns. 2 Severe multiorgn filure cn include circultory collpse, neurologicl dysfunction, renl filure, rhbdomyolysis, liver filure, nd disseminted intrvsculr cogultion. Militry service personnel, with strenuous physicl ctivities nd physicl fitness requirements, re t high risk for EHI when operting in wrm environments, especilly if they re poorly cclimtized. 8 The Mrine Corps Recruit Depot t Prris Islnd, South Crolin (MCRD-PI) trins 15,000 to 20,000 recruits ech Deprtment of Preventive Medicine nd Biometrics, Uniformed Services University of the Helth Sciences, Bethesd, MD The opinions or ssertions contined herein re the privte ones of the uthors nd re not to be construed s officil or reflecting the views of the U.S. Deprtment of Defense or the Uniformed Services University of the Helth Sciences. This mnuscript ws received for review in October The revised mnuscript ws ccepted for publiction in June yer in 12-week bsic militry trining course, nd recruits who trin in its wrm nd humid climte hve been subjects of mny studies of EHI. 6,7,9 12 These recruits re mediclly screened to eliminte those with chronic illness nd re generlly helthy young dults ( 90% ges yers). The trining progrm includes pproximtely 2 hours ech dy of conditioning exercise, which often involve runs of 1 to 5 miles. Their lives re extremely regimented, nd they undergo the sme trining ctivities, wer the sme clothing, et the sme food, etc., in ddition to bstinence from smoking, lcohol, nd ny vehiculr driving during the entire bsic trining period. This cse-control study ws conducted on recruit EHI cse subjects to ssess clinicl fctors tht re ssocited with, or predict, hospitliztion s prt of medicl tretment. An understnding of the clinicl fctors predicting EHI hospitliztion my id helth cre personnel in mnging nd delivering prompt nd pproprite cre to those who re more seriously ill. Predictors of hospitliztion t MCRD-PI, where EHI is quite common but serious complictions re rre, cn provide guidnce in ssessing severity of illness nd the need for specific therpy to prevent serious complictions. Methods The subjects of this cse-control study consisted of ll mle Mrine Corps recruits in bsic trining t MCRD-PI during 1988 to 1992 who received medicl cre for EHI. The helth cre for these recruits is firly uniform, nd methods of dignosis nd identifiction of EHI cses t MCRD-PI hve been detiled elsewhere. 6,7 Of 88,000 recruits in bsic trining during the 5-yer period, 650 visited the medicl clinic or hospitl for EHI with symptoms rnging from mentl slowness, wobbly git, nd/or dehydrtion to syncope, confusion, disorienttion, nd/or unconsciousness, usully with elevted rectl temperture. EHI ws dignosed by locl medicl providers on the bsis of the bove symptoms ssocited with exercise nd without other obvious cuse. The outcome mesured in this study is hospitliztion for EHI. Cse subjects were recruits who were seen t the clinic or hospitl emergency room with n EHI dignosis nd were hospitlized t lest overnight. Control subjects were recruits who were seen t the clinic or hospitl emergency room with n EHI dignosis nd were not hospitlized overnight. Subjects were identified nd some clinicl informtion ws obtined through Nvy medicl surveillnce report forms (NAVMED 6500). 6,7 In ddition, concurrent review of ll clinicl, lbortory, nd hospitl records identified dditionl subjects nd clinicl informtion not included in the NAVMED 6500 forms. Demogrphic nd nthropometric dt were obtined for ech recruit with EHI from the Mrine Corps Automted Recruit Mngement System. 169

2 170 Hospitliztion in EHI TABLE I SELECTION OF STUDY POPULATION FROM EHI CASES DURING RECRUIT BASIC TRAINING AT MCRD-PI, Chrcteristic Hospitl (cse subjects) No. of EHI cses Outptient (control subjects) Totl No. eligible No. excluded No. included in study Women were excluded due to lck of hospitlized cses during The vribles included for study re shown in Tble III, which lso gives the ctegoriztions used in the nlyses. These dt were obtined through review of the clinicl records of ech subject nd of the lbortory logbooks t the Beufort Nvl Hospitl. The men vlues of continuous vribles were compred for hospitlized cse subjects nd outptient control subjects with sttisticl significnce determined using Student s t test for independent smples. All vribles were ctegorized, bsed upon grdes of severity, into two to four levels. In univrite nlyses, we clculted odds rtios nd 95% confidence limits for ech vrible, compring ech level to referent level. In some nlyses, missing vlues were recoded to the referent ctegory so s mny subjects s possible were vilble for inclusion in multivrite regression procedures. We combined these missing vlues with the referent level under the ssumption tht they were not obtined or recorded (usully lbortory tests) becuse they were presumed to be norml. Multivrite nlyses were performed using stepwise multivrite logistic regression models to identify those vribles most importnt in independently predicting EHI hospitliztion. Stepwise logistic regression sequentilly considers ech vrible nd rrives t finl prsimonious model consisting of the vribles tht best predict being cse subject (s opposed to control subject). 13 In the logistic models, vribles were represented s indictor vribles, whereby ech ctegory ws coded 0 or 1 to represent the level s bsence or presence, respectively. These nlyses were conducted using SPSS 8.0 for Windows. TABLE II DESCRIPTIVE STATISTICS OF POTENTIAL RISK FACTORS IN HOSPITALIZED CASE AND OUTPATIENT CONTROL EHI PATIENTS, MCRD-PI, Cse Subjects Control Subjects Vrible n Rnge Men SE n Rnge Men SE p Age (yers) Height (m) Weight (kg) Body mss index (kg/m 2 ) Amnesi durtion 35 b (57%) (16%) (minutes) Disorienttion durtion 42 b (69%) (15%) (minutes) Minimum systolic blood pressure (mm Hg) Mximum temperture ( F) Mximum BUN (mg/dl) Mximum cretinine (mg/dl) Mximum sodium Minimum sodium Mximum potssium Minimum potssium Minimum HCO Minimum glucose (mg/dl) Mximum CK (U/L) ,000 10,672 4, ,000 1, Mximum uric cid , ( mol/l) Mximum AST (U/L) , Mximum LDH (U/L) , , p Vlue of comprison of mens t test. b N number (%) non-zero.

3 Hospitliztion in EHI 171 TABLE III FREQUENCY DISTRIBUTIONS, OR, AND 95% CONFIDENCE INTERVALS FOR RISK FACTORS ASSESSED IN RELATION WITH HOSPITALIZED CASE AND OUTPATIENT CONTROL EHI PATIENTS, MCRD-PI, Cse Subjects (n 61) Control Subjects (n 504) Vrible No. (%) No. (%) OR 95% Confidence Intervl Age (yers) 23 (men 24.8) 10 (16) 36 (7) (13) 56 (11) (36) 194 (39) (34) 214 (43) 1.0 Referent Missing 4 (1) Rce Cucsin 43 (71) 306 (61) Other 18 (30) 198 (39) 1.0 Referent Height (m) (39) 167 (33) (49) 226 (45) (10) 64 (13) 1.0 Referent Missing 1 (2) 47 (9) Weight (kg) (36) 146 (30) (53) 231 (46) (10) 77 (15) 1.0 Referent Missing 1 (2) 50 (10) Body mss index (kg/m 2 ) (44) 157 (31) (39) 208 (41) (15) 87 (17) 1.0 Referent Missing 1 (2) 52 (10) Worst Neurology,b D 10 (16) 10 (2) C 11 (18) 10 (2) B 15 (25) 70 (14) A 12 (20) 210 (42) 1.0 Referent Missing 13 (21) 204 (41) Amnesi durtion (minutes) (33) 18 (4) (25) 63 (13) None/missing 26 (43) 423 (84) 1.0 Referent Minimum orienttion 0 22 (36) 56 (11) (31) 81 (16) (31) 247 (49) 1.0 Referent Missing 1 (2) 121 (24) Disorienttion durtion (minutes) (33) 5 (1) (13) 5 (1) (23) 68 (14) None/missing 19 (31) 426 (84) 1.0 Referent Minimum systolic blood pressure (mm Hg) (21) 26 (5) (57) 237 (47) (20) 171 (34) 1.0 Referent Missing 1 (2) 70 (14) Syncope Yes 41 (67) 149 (30) No/missing 20 (33) 355 (70) 1.0 Referent Mximum body temperture ( F) (57) 21 (4) (26) 287 (57) (16) 165 (33) 1.0 Referent Missing 31 (6) Mximum BUN (mg/dl) 26 9 (15) 25 (5) (82) 295 (59) 1.0 Referent Missing 2 (3) 184 (36) (continues)

4 172 Hospitliztion in EHI TABLE III (CONTINUED) Vrible No. (%) No. (%) OR 95% Confidence Limits Mximum cretinine (mg/dl) (41) 52 (10) (30) 102 (20) (26) 166 (33) 1.0 Referent Missing 2 (3) 184 (37) Mximum sodium (48) 74 (15) (49) 254 (50) 1.0 Referent Missing 2 (3) 176 (35) Minimum sodium (8) 17 (3) (89) 310 (62) 1.0 Referent Missing 2 (3) 177 (35) Mximum potssium (38) 38 (8) (59) 291 (58) 1.0 Referent Missing 2 (3) 175 (35) Minimum potssium (38) 26 (5) (59) 301 (60) 1.0 Referent Missing 2 (3) 177 (35) Minimum HCO (28) 36 (7) (33) 98 (19) (36) 191 (38) 1.0 Referent Missing 2 (3) 179 (36) Minimum glucose (mg/dl) (21) 37 (7) (75) 285 (57) 1.0 Referent Missing 2 (3) 182 (36) Mximum cretine phosphokinse (U/L) 4, (26) 14 (3) ,200 3, (21) 57 (11) , (18) 44 (9) (25) 112 (22) 1.0 Referent Missing 6 (10) 277 (55) Mximum uric cid ( mol/l) (34) 14 (3) (25) 105 (21) (13) 100 (20) 1.0 Referent Missing 17 (28) 285 (57) Mximum AST (U/L) (33) 20 (4) (12) 55 (11) (43) 151 (30) 1.0 Referent Missing 8 (13) 278 (55) Mximum LDH (U/L) (41) 22 (4) (28) 84 (17) (21) 129 (26) 1.0 Referent Missing 6 (10) 269 (53) Results Cse Subjects (n 61) Vribles with missing vlues were recoded s prt of referent ctegory. b See text for definitions. Tble I depicts the selection of the study popultion. Of the 650 EHI cses reported in recruits t MCRD-PI during 1988 to 1992; 565 were men nd 85 were women. Femle EHI cse subjects were excluded becuse they hd no hospitliztions. Sixty-one of 565 mle recruits were hospitlized for EHI, providing 61 hospitlized cse subjects nd 504 outptient control subjects for this cse-control nlysis of predictors of hospitliztion in EHI. Control Subjects (n 504) Tble II presents descriptive sttistics (number, rnge, men, SE, comprison of mens t test p vlue) of the potentil risk fctors by cse or control sttus. The hospitlized cse subjects nd outptient control subjects shred similr men ge, height, weight, nd body mss index (body mss index weight/height 2 ). More hospitlized cse subjects thn outptient control subjects experienced mnesi nd/or disorienttion during their EHI episode (57% vs. 16% nd 69% vs. 15%, respectively) (p 0.001), nd verge durtion ws longer for

5 Hospitliztion in EHI 173 hospitlized cse subjects thn for outptient control subjects who hd mnesi or disorienttion (40 vs. 11 minutes nd 193 vs. 30 minutes, respectively). The hospitlized cse subjects lso hd higher verge mximum rectl temperture thn the outptient control subjects (105.3 vs F) nd lower verge minimum systolic blood pressure. Serum electrolytes showed significntly higher mximum sodium, lower minimum sodium, nd lower minimum potssium in hospitlized cse subjects compred with outptient control subjects. Averge minimum serum bicrbonte (HCO 3 ) nd glucose levels were significntly lower in hospitlized cse subjects thn in outptient control subjects, nd verge mximum serum cretinine levels were higher, wheres verge mximum blood ure nitrogen (BUN) levels showed differences tht were not sttisticlly significnt. Averge mximum serum muscle nd liver enzyme levels were ll significntly higher in hospitlized cse subjects thn in outptient control subjects: cretine kinse (CK; 10,600 vs. 1,400), uric cid (625 vs. 450), sprtte minotrnsferse (AST; 151 vs. 58), nd lctte dehydrogense (LDH; 535 vs. 291). Tble III shows the frequency distribution, odds rtios (OR), nd 95% confidence intervls for risk fctors ssessed in reltion to EHI hospitliztion by cse or control sttus. Nineteen of the 24 nlyzed vribles were ssocited significntly with risk for EHI hospitliztion. Older ge ( 23 yers) showed significntly higher risk for EHI hospitliztion (OR, 2.8) thn in younger recruits (17 18 yers). Rce, height, weight, nd body mss index were not significntly ssocited with risk for hospitliztion in EHI. Neurologicl vribles included worst neurologicl sttus, mnesi, nd orienttion (wreness of person, plce, nd time; score 3 defines disorienttion). Neurologicl sttus ws ctegorized into four levels: (A) norml, slow menttion, or drowsy; (B) confused but coopertive; (C) delirious or confused nd uncoopertive; nd (D) obtunded or comtose. Amnesi ws ssessed s loss of memory of events beyond short period (3 minutes) of syncope. All neurologicl vribles showed very strong significnt ssocitions with hospitliztion in EHI (ORs for worst cse vs. norml rnged from 5 to 90). Dehydrtion nd renl function vribles included minimum systolic blood pressure, exertionl syncope, nd mximum BUN nd serum cretinine. Ech of these showed significnt ssocitions with hospitliztion for EHI (ORs, 3 12). In ddition, mximum rectl temperture of 106 F nd bove ws highly predictive of hospitliztion for EHI (OR, 29), but lower levels of elevted temperture showed no ssocition. Serum electrolytes showed some significnt ssocitions with hospitliztion for EHI, prticulrly low potssium, high sodium, nd low bicrbonte. Low serum glucose lso ws ssocited significntly with hospitliztion for EHI. Elevted serum muscle nd liver enzymes ll were ssocited strongly with hospitliztion for EHI (ORs, 13 24, compring worst cse with norml levels for mximum CK, uric cid, AST, nd LDH). Extensive multivrite nlysis ws conducted using stepwise logistic regression models. All vribles were included in the initil models, nd nlyses were conducted both with nd without inclusion of the missing vlues in predicting hospitlized cse vs. outptient control sttus. Inclusion nd exclusion of missing vlues, different estimtion methods, different sets of vribles, nd differing inclusion criteri nd methodology (forwrd vs. bckwrd) ll consistently led to the finl model presented here. For the finl model using stepwise logistic regression nlyses, ll 565 recruits were included (by recoding missing vlues to the referent level). The most stble nd predictive model retined six vribles (from the full model with 24 vribles) s predictive of hospitliztion in EHI: disorienttion durtion, mximum rectl temperture, minimum systolic blood pressure, mximum serum LDH nd cretinine vlues, nd minimum serum potssium vlues (Tble IV). The model correctly predicted 59% of hospitliztions (sensitivity) nd 99% of nonhospitliztions (specificity) mong recruits. Discussion Although most clinicl vribles studied were ssocited with hospitliztion for EHI, in the multivrite nlysis we show tht hospitliztion t MCRD-PI ws predicted well using only three clinicl (rectl temperture, systolic blood pressure, nd disorienttion) nd three lbortory (serum LDH, cretinine, nd potssium) vribles. These vribles ech reflect different spects of the clinicl presenttion nd severity of EHI (temperture response, crdiovsculr nd neurologicl sttus, liver/ muscle cell lysis, renl function, nd electrolyte chnges). Erly ssessment of EHI severity nd identifiction of the need for more thn routine outptient tretment of EHI is n importnt gol for medicl providers. Hospitliztion does not directly ssess the severity of illness, rther it ssesses the subjective decision of the locl medicl provider tht incorportes perception of severity nd other fctors tht my vry from one clinicl setting to the next. Prediction of hospitliztion, therefore, predicts medicl prctice ptterns tht re relted to the severity of illness. In Mrine Corps recruit trining t MCRD-PI, there hs been gret success in preventing serious complictions nd deth in EHI despite its common occurrence nd n environmentlly hzrdous trining environment. Approximtely 11% of cse subjects were hospitlized, nd there were no cses of severe liver or kidney filure, severe rhbdomyolysis, or disseminted intrvsculr cogultion in 15 yers of surveillnce. 6,7,9 11 The prediction of this prctice pttern, therefore, cn be useful for medicl providers in mnging EHI in helthy young dults. This study hs severl strengths which include ccurte surveillnce for EHI in lrge, well-defined exercising popultion with stndrdized trining ctivities nd circumstnces. The homogeneity of the popultion, trining environment, nd helth cre system helps focus on specific issues relting to EHI nd hospitliztion. However, it hs the disdvntge of being less representtive of the generl popultion nd of missing importnt fctors tht re excluded from the recruit trining environment, such s lcohol nd tobcco use, older ge groups, nd chronic illness nd medictions. In ddition, we could not study women. Other weknesses of the study include those relted to use of existing records, existing dt, nd the inbility to provide fully stndrdized prospective pproch to evlution nd dignosis with specific set of clinicl nd lbortory studies obtined on every EHI cse. The six predictor vribles for hospitliztion llow for reltively simple index tht cn be used to evlute EHI severity nd need for hospitl cre. We developed n EHI hospitliztion

6 174 Hospitliztion in EHI TABLE IV FINAL STEPWISE LOGISTIC REGRESSION MODEL INDICATING VARIABLES RETAINED IN PREDICTING HOSPITALIZATION IN EHI PATIENTS, MCRD-PI, Vrible SE OR 95% Confidence Intervl Disorienttion durtion (minutes) None/missing 1.0 Mximum body temperture ( F) or missing 1.0 Minimum systolic blood pressure (mm Hg) or missing 1.0 Mximum LDH (U/L) or missing 1.0 Minimum potssium or missing 1.0 Mximum cretinine (mg/dl) or missing 1.0 Intercept risk score (Tble V) by ssigning score of 1 to ech pplicble ctegory of the six vribles, with score of 2 ssigned to disorienttion for 30 or more minutes, nd then summing the ssigned scores. The hospitliztion risk score derived from these vribles thus rnges from 0 to 7. A higher score indictes higher probbility for hospitliztion nd presumbly higher severity of EHI. If we use score of 2 or more s indicting need for hospitliztion, then this score provides sensitivity of 87% nd specificity of 91%, with likelihood rtio of 9.7 when pplied to these dt (Tble VI). For exmple, using the hospitliztion risk score s the sole bsis for hospitliztion in these study ptients, 8 (13%) of the 61 TABLE V SIX VARIABLES COMPOSING THE EHI HOSPITALIZATION RISK SCORE Vrible Score Disorienttion durtion (minutes) Minimum systolic blood pressure (mm Hg) Mximum body temperture ( F) Minimum potssium Mximum LDH (U/L) Mximum cretinine (mg/dl) All vlues other thn those indicted in the tble re scored 0. hospitlized cse subjects would hve missed hospitliztion nd 45 (9%) of the 504 outptient control subjects would hve been hospitlized. Although this risk score ppers to ccurtely predict hospitliztion in these ptients t Prris Islnd, its generlizbility is yet unproven. The Prris Islnd trining environment is unique in its hydrtion policy nd immedite medicl cre for EHI, which my ffect the predictbility of these vribles in other circumstnces. Considertion of these six clinicl nd lbortory fctors (temperture response, crdiovsculr nd neurologicl sttus, liver/muscle cell lysis, renl function, nd electrolyte chnges) should be used in ssessing EHI severity in ny setting, lthough the clinicl effectiveness of the proposed quntittive scoring using these specific vribles hs not been estblished. We recommend tht use of this hospitliztion risk score be vlidted t this nd other trining centers. This cse-control study of routinely recorded medicl informtion in EHI cses t MCRD-PI hs ssessed clinicl fctors ssocited with hospitliztion, developed predictive model for hospitliztion, nd provided n EHI hospitliztion risk scoring system. These results my fcilitte rpid ssessment by medicl cregivers of severity nd need for hospitliztion when pplied to EHI in previously helthy young dults. Prompt nd efficient delivery of pproprite medicl cre cn prevent unnecessry complictions, dignostic tests, medicl costs, prolonged tretment, need for rehbilittion, nd deth in EHI cses. Acknowledgments We thnk the personnel of the Beufort Nvl Hospitl nd the Prris Islnd Mrine Corps Recruit Depot who ided in collection of these dt.

7 Hospitliztion in EHI 175 TABLE VI DISTRIBUTION AND LIKELIHOOD RATIOS (LR) FOR THE EHI HOSPITALIZATION RISK SCORE A Hospitlized Cse Subjects Outptient Control Subjects Score No. Percent No. Percent LR b Totl For hospitliztion t score 1: sensitivity, 92%; specificity, 66%; LR, 2.7. For hospitliztion t score 2: sensitivity, 87%; specificity, 91%; LR, 9.7. For hospitliztion t score 3: sensitivity, 62%; specificity, 98%; LR, 35. b The LR is the percentge of hospitlized cses t tht level divided by the percentge of outptient cses t tht level. This is the multiplying fctor for person scoring t tht level in predicting hospitliztion vs. outptient tretment: O 1 LR O 0, where O 1 is the post-test odds, P 1 is the post-test probbility, O 0 is the pretest odds, nd P 0 is the pretest probbility nd O P/(1 P) nd P O/(1 O). P 0 is the prevlence of hospitliztion (i.e., 11% of our cses were hospitlized); for score of 2: P O ; O P / Thus, t score 2 the probbility for hospitliztion increses from the verge of 11% to 55%; for score 4 it increses to 96%. This project ws supported in prt by Uniformed Services University of the Helth Sciences Grnts RO87CI nd RO87HR nd by U.S. Army Reserch Institute of Environmentl Medicine Contrct GY87CV. References 1. Shibolet S, Coll R, Gilt T, Sohr E: Hetstroke: its clinicl picture nd mechnism in 36 cses. Q J Med 1967; 36: Knochel JP: Het stroke nd relted het stress disorders. Dis Mon 1989; 35: Grdner JW, Krk JA: Ftl rhbdomyolysis presenting s mild het illness in militry trining. Milit Med 1994; 159: Wyndhm CH: Het stroke nd hyperthermi in mrthon runners. Ann N Y Acd Sci 1977; 301: Brown JR: Het illness nd Army recruits. Lncet 1986; 1: Krk JA, Burr PQ, Wenger CB, Gstldo E, Grdner JW: Exertionl het illness in Mrine Corps recruit trining. Avit Spce Environ Med 1996; 67: Grdner JW, Krk JA, Krnei K, et l: Risk fctors predicting exertionl het illness in mle Mrine Corps recruits. Med Sci Sports Exerc 1996; 28: Bricknell MC: Het illness in the rmy in Cyprus. Occup Med (London) 1996; 46: Minrd D, Belding HS, Kingston JR: Prevention of het csulties. JAMA 1957; 165: Minrd D: Prevention of het csulties in Mrine Corps recruits. Milit Med 1961; 126: Costrini AM, Pitt HA, Gustfson AB, Uddin DE: Crdiovsculr nd metbolic mnifesttions of het stroke nd severe het exhustion. Am J Med 1979; 66: Surber B, Steele K: Het illness. US Nvy Med 1983; Hosmer DW, Lemeshow S: Applied Logistic Regression. New York, NY, John Wiley & Sons, 1989.