1 Department of Defense Center for Deployment Health Research, Naval Health Research Center, San Diego, CA.
2 Deployment Environmental Surveillance Program, US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD.
3 Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA.
Received for publication October 16, 2003; accepted for publication January 16, 2004.
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ABSTRACT |
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environmental exposure; hospitalization; military medicine; morbidity; occupational exposure; Persian Gulf syndrome; veterans
Abbreviations: Abbreviations: CI, confidence interval; DoD, Department of Defense; ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification; OR, odds ratio.
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INTRODUCTION |
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Despite in-theater successes, reports of postwar illness among veterans have resulted in much research into the postwar health of Gulf War veterans in the last decade since the war. There have been numerous studies demonstrating that Gulf War veterans are more likely to self-report symptoms (611) and adverse pregnancy outcomes (12) than their military peers. However, large epidemiologic studies have found no definitive evidence to suggest excess morbidity among Gulf War veterans as measured by hospitalizations (1315), mortality due to diseases (1619), or birth defects among livebirths in active-duty members within 2 years of the Gulf War (20). Additionally, epidemiologic studies focusing on the health impacts of specific wartime exposures compared Gulf War veterans and found no excess in hospitalizations for those personnel possibly exposed to the smoke from Kuwaiti oil well fires (21) or those personnel possibly exposed to nerve agents released as a result of the US demolition of a munitions depot at Khamisiyah, Iraq (22, 23). However, because electronic data were unavailable, to date there have been no large investigations of morbidity during the war. This retrospective report is the first to summarize the epidemiologic findings obtained from examining more than 28,000 paper records of US and coalition in-theater hospitalizations that were medically evacuated to medical treatment facilities during the Gulf War.
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MATERIALS AND METHODS |
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Gulf War exposure data
Environmental exposures, such as Kuwaiti oil well fire smoke (21), depleted uranium (26, 27), dust (28), and possible exposure to nerve agents after the US-led demolition of a large munitions depot at Khamisiyah, Iraq (29, 30), have been suggested as possible factors affecting the postwar health of veterans. As part of our investigation of in-theater hospitalizations, estimates of possible exposure to the Kuwaiti oil well fire smoke and the 2002 plume modeling of the destruction of the Khamisiyah munitions depot are included in this report (2123). Although these data are described in detail elsewhere (2123), a brief description is provided.
The Iraqi Army ignited over 600 oil wells during their withdrawal from Kuwait in 1991 (21, 31). The resulting massive clouds of smoke raised concerns that US troops possibly exposed to these pollutants might experience adverse health effects. In response, the US Army Center for Health Promotion and Preventive Medicine in collaboration with the National Oceanic and Atmospheric Administration/Air Resources Laboratory estimated 24-hour unit exposure data. These data were overlaid onto troop location data using a geographic information system to produce troop unit exposure estimates throughout the period that the fires burned (21).
In June 1996, the DoD announced that the United Nations strongly suspected that rockets equipped to carry chemical weapons had been destroyed in March 1991 by US forces near Khamisiyah, Iraq (30). This prompted meteorologic and dispersion modeling of the possible release of sarin and cyclosarin to model estimated hazard areas. These data were overlaid onto troop location data to identify those personnel possibly exposed to nerve agents from the destruction of Khamisiyah in March 1991. The final report, released in April 2002, identified 101,752 Gulf War veterans as having been possibly exposed in the hazard areas created by the destruction of munitions at Khamisiyah (30).
Gulf War hospitalization data
In June 1998, the Office of the Special Assistant to the Deputy Secretary of Defense for Gulf War Illnesses began work on a records database of all Gulf War inpatient hospital treatment records archived at the National Personnel Records Center in St. Louis, Missouri (32). These archived records were thought to represent approximately 75 percent of the total reported admissions at 44 Army hospitals, 15 Air Force hospitals, and five or more Navy hospitals in the Kuwaiti theater of operations (32). Therefore, additional efforts were made to investigate for inpatient records of Gulf War evacuees to military hospitals in Europe who might not have corresponding in-theater admission records (32). This work concluded in October 1999 with the identification of 22,444 admissions occurring in the Kuwaiti theater of operations and 5,563 evacuated admissions to hospitals in Europe.
In November 2000, at the direction of the Special Assistant to the Deputy Secretary of Defense for Gulf War Illnesses, a team of deployment health specialists and medical record abstractors began reviewing all archived Gulf War inpatient treatment records to determine if the existing archived inpatient paper records contained sufficient information to conduct research on the inpatient hospitalization experience of Gulf War veterans (32). This work resulted in the construction of a database that could be used to investigate in-theater hospitalizations during the 1991 Gulf War. Abstracted hospitalization data were reviewed twice in their entirety and run through a series of quality assurance steps to achieve the greatest possible accuracy. These data included Social Security number, admission date, patient identification, record identification, and associated medical discharge diagnoses coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) (33). Additionally, these data contained demographic and other descriptive data, including race, sex, date of birth, service branch, marital status, military component, military rank, DoD primary military occupational specialty, and country code, which identified the nationality of all patients. For the purposes of this report, in-theater hospitalizations will be used to encompass those hospitalized within the Kuwaiti theater of operations and those medically evacuated to DoD treatment facilities in Europe.
Study outcomes
Investigation of outcomes included in-theater hospitalization for any cause, frequency of in-theater hospitalization with a diagnosis in any of 15 broad ICD-9-CM diagnostic categories, the 10 most common in-theater three-digit diagnoses, the overall five most common in-theater three-digit diagnoses for each ICD-9-CM diagnostic category, and the five most common in-theater three-digit diagnoses by broad occupational category. Additionally, the top 10 three-digit hospital diagnoses among other coalition forces were investigated. Hospital admissions were scanned in chronologic order for the diagnostic code of interest. Frequency and regression analyses were based on unique personnel having at least one diagnosis captured from the hard-copy medical records.
Statistical analyses
Following descriptive investigation of the population characteristics of those hospitalized and not hospitalized in theater, univariate analyses were performed to assess the significance of associations between demographic, exposure, and deployment variables and hospitalization. A multivariable model was developed to further assess significant associations, collinearity, and confounding, while simultaneously adjusting for all other variables in the model. Using multivariable logistic regression, we further investigated the in-theater hospitalization experience of Gulf War veterans during the period from August 1, 1990, to July 31, 1991. A manual backward stepwise elimination model approach was used on the saturated logistic regression model to arrive at a reduced model by removing those variables that were insignificant at the alpha = 0.05 level and not confounding the other measures of association. The final model included only those variables independently associated with the outcome of interest with p < 0.05. Statistical modeling, producing adjusted odds ratios and associated 95 percent confidence intervals, was performed using SAS version 8.0 software (SAS Institute, Inc., Cary, North Carolina).
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RESULTS |
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The multivariable logistic regression model revealed significant associations between demographic variables and in-theater hospitalization after adjusting for all other variables in the model (table 5). Women had 1.44 times the odds of hospitalization compared with men (odds ratio (OR) = 1.44, 95 percent confidence interval (CI): 1.37, 1.51). Married personnel were at increased odds of in-theater hospitalization compared with nonmarried personnel (OR = 1.46, 95 percent CI: 1.41, 1.51), and Reservists or National Guard personnel were at increased odds of hospitalization when compared with active duty personnel (OR = 1.55, 95 percent CI: 1.48, 1.62). Those personnel with prewar hospitalizations had increased odds of in-theater hospitalization when compared with those without an inpatient record from the previous year (OR = 1.80, 95 percent CI: 1.72, 1.89). Personnel aged 2326 years (OR = 0.95, 95 percent CI: 0.91, 0.99) and those aged 2732 years (OR = 0.89, 95 percent CI: 0.85, 0.94) had decreased odds of in-theater hospitalization when compared with personnel 1722 years of age. When compared with the Army, all other branches of service displayed lower odds of hospitalization, as did officers when compared with enlisted members (commissioned: OR = 0.56, 95 percent CI: 0.52, 0.59; warrant officer: OR = 0.84, 95 percent CI: 0.74, 0.95).
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When compared with infantry, gun crew, and seaman (combat) specialists, health-care workers had 1.56 times the odds of in-theater hospitalization (95 percent CI: 1.46, 1.65), service and supply handlers had 1.44 times the odds (95 percent CI: 1.37, 1.52), craft workers had 1.37 times the odds (95 percent CI: 1.26, 1.49), and functional support had 1.10 times the odds of in-theater hospitalization (95 percent CI: 1.04, 1.16) (table 5). From these five categories, unspecified disorders of the back (ICD-9-CM code 724) and noninfectious gastroenteritis and colitis (ICD-9-CM code 558) were the most common. General symptoms, such as sleep disturbance or drowsiness (ICD-9-CM code 780), were in the top five most common three-digit diagnoses for health-care workers, functional support personnel, and service and supply handlers (table 6).
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DISCUSSION |
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As part of our continuing efforts to assess plausible relations among potential Gulf War exposures and health outcomes, we examined 30,740 diagnoses among 18,631 US personnel who were hospitalized during the Gulf War. The number of hospitalizations was proportional to the number of service members in the region during the 1-year period of operations (figure 1). Many of the diagnoses were of general symptoms, such as sleep disturbance or drowsiness, which may be reflective of a war setting and harsh environmental conditions. Furthermore, the categories of "injury and poisoning" and "musculoskeletal system disorders" comprised nearly 40 percent of the diagnoses (table 2). The five most common diagnoses in these categories reflected dislocations, sprains, and strains of knees, ankles, joints, and backs. Digestive system diseases made up the third most frequently diagnosed category (12.6 percent). Over 40 percent of the diagnoses in this category were from other noninfectious gastroenteritis and colitis diagnoses. This condition was also identified as the most frequently diagnosed (5.1 percent) among the top 10 any-cause diagnoses (table 3). The top 10 most frequent diagnoses among US allies were similar to those among US personnel except for diagnoses consisting of open wounds or complications of medical care, likely indicative of needed emergency services (table 4).
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We investigated five robust occupational categories that were found to be at increased odds of in-theater hospitalization when compared with combat specialists (table 6). Because of the frequency with which these diagnoses occurred in these analyses, it is not surprising that unspecified disorders of the back and noninfectious gastroenteritis and colitis were identified in the top five diagnoses among each occupational category investigated. However, injuries, including sprains, strains, and dislocations of the knee and other joints, were common to combat and support personnel. Symptoms involving the respiratory system, asthma, and general sleep disturbance or drowsiness were common to health-care specialists, functional support specialists, and service and supply handlers.
This report has a number of limitations that should be noted. First, these data are not a complete assessment of hospitalizations occurring in theater during the Gulf War. For example, some US personnel were treated in host nation hospitals run by Saudi Arabia, and records from these facilities are not available. Additionally, the exact number of admissions to DoD military hospitals in the Kuwaiti theater of operations is uncertain. We report on approximately 22,000 hospitalizations in the Kuwaiti theater of operations that represent approximately 75 percent of the total reported admissions by the Air Force (n = 3,494), the Navy (n = 6,613), and the Army (n = 19, 941) (32). Furthermore, this investigation focused on morbidity severe enough to require hospitalization. It is possible that, in a wartime setting, some injuries and illnesses ordinarily resulting in a hospitalization while in garrison or on normal duty may be treated in the field or at outpatient or mobile clinics; therefore, our ability to examine medical treatment, particularly during the combat period, is diminished.
Although extensive efforts were made to accurately model potential exposure to oil well fire smoke and Khamisiyah nerve agents, acquiring precise individual-level exposure data is challenging, and presumed exposures should be viewed with some caution (22, 23). Additionally, we were not able to investigate or control for other exposures that may have had an effect on the outcomes reported here, such as smoking, alcohol use, stress, and jet fuel. Furthermore, the use of logistic regression does not take into account person-time at risk for an event the way survival analytical techniques would. Although we know that personnel came and went during the conflict, there was not enough confidence with theater dates at an individual level to employ a time-to-event type modeling approach.
Despite these limitations, these data offer the first large epidemiologic investigation of morbidity occurring during the 1991 Gulf War. Hospitalization data alone may not represent the entire spectrum of health outcomes. However, these data reflect a more contemporaneous and objective measure of morbidity than later self-reports of symptoms and illnesses might. The use of sophisticated meteorologic and dispersion modeling techniques was integrated with unit tracking to identify those possibly exposed to the potential low levels of nerve agent in the hazard areas near Khamisiyah and those possibly exposed to Kuwaiti oil well fire smoke. The combination of these exposure data with in-theater hospitalization data presents the first objective assessments of associations between acute morbidity severe enough to warrant hospitalization and potentially hazardous wartime exposures. Prior investigations also were insufficient at investigating morbidity in Reserve and National Guard populations, because these subpopulations left military service after the war and were no longer visible through the DoD health-care system. In this report, we were able to investigate Reserve and National Guard members in the same context as we were able to investigate active-duty members.
In summary, our analyses demonstrated important independent factors associated with in-theater hospitalization during the 1991 Gulf War. We found that the distribution of diagnoses was consistent with the physical stress and harshness of a combat environment, and that subgroups consisting of combat and support personnel were frequently diagnosed with similar conditions. There were no unusual patterns in the number of hospitalizations when compared with troop strength. It should be reassuring to US personnel that these data suggest that US military personnel possibly exposed to oil well fire smoke or chemical warfare agents in the Khamisiyah hazard areas were not at increased odds of in-theater morbidity when compared with nonexposed US military personnel. The lessons of the Gulf War have encouraged movement toward force health protection within the DoD (3537). This movement, along with technologic advancements, will help to standardize reporting of health outcomes on the battlefield, to alleviate concerns of veterans and the public in a much more timely manner, and to guide health-care resources quickly and efficiently to those personnel in need of care.
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ACKNOWLEDGMENTS |
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The authors thank Michael J. Boyle, Thomas A. Rupp, Dr. Francis L. ODonnell, and Dr. Michael E. Kilpatrick from the Deployment Health Support Directorate (formerly Office of Special Assistant for Gulf War Illnesses) for years of dedicated work to capture these in-theater hospitalization data. The authors also thank Michael A. Dove and Scott L. Seggerman from the Management Information Division, Defense Manpower Data Center, Seaside, California, for providing Gulf War veteran deployment data. They thank Chris Weir, Jeff Kirkpatrick, and Warren Wortman from the Deployment Environmental Surveillance Program of the US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, Maryland, for providing troop location and exposure data. The authors appreciate the support of Dr. Gary Gackstetter and Dr. Tomoko Hooper of the Uniformed Services University of Health Sciences, Bethesda, Maryland, and the support of the Henry M. Jackson Foundation for the Advancement of Military Medicine, Rockville, Maryland.
The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the US Government.
This research has been conducted in compliance with all applicable federal regulations governing the protection of human subjects in research (protocol no. 31283).
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NOTES |
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REFERENCES |
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