What are the new findings?

In 2023, injuries, mental health disorders, and musculoskeletal diseases were the medical conditions associated with the most medical encounters, greatest numbers of service members affected, and highest numbers of hospital days. Major category conditions increased overall by about 17% compared to 2022, and medical encounters increased by 18%. COVID-19 accounted for no more than 0.3% of total member medical encounters and hospital bed days among active component service members in 2023.

What is the impact on readiness and force health protection?

The major condition categories in this report present health challenges among U.S. active component service members that can affect force readiness. Investigating morbidity and health care burdens enables prioritization of relevant health conditions, and their primary causes, for appropriate resource allocation and proactive management of potential health events through timely intervention, research, and resources. Development and consistent implementation of policies and safeguards is critical for reducing the burden of diseases that affect readiness.

Background

MSMR’s annual burden of disease reports are designed to provide accurate estimations of the general health status of U.S. military personnel, for prioritization of effective interventions with measurable impacts on force readiness.¹

In these reports, diagnoses are grouped to inform our readership of the major factors and variables each year affecting health care provision within the Military Health System. Although burden of disease within a health care system can be classified into several categories, the majority of the disease burden globally comes from non-communicable diseases, with communicable diseases the second-most prevalent, followed by maternal, neonatal and nutritional diseases, and subsequently injuries.²

To broadly describe the morbidity burden among active component service members, MSMR has used, since 2001, a classification system derived from the Global Burden of Disease Study,^3,4 a systematic, scientific effort that began 30 years ago to quantify the magnitude of all major diseases, their risk factors, and intermediate clinical outcomes in a highly standardized manner. This systematic classification enables comparisons between populations and health problems over time.⁵ MSMR utilizes the GBD classification system in combination with an International Classification of Diseases, 10th Revision, Clinical Modification chapter-based system for categorization of hospitalizations and ambulatory visits among the MHS population.

To improve the usefulness of this information, these classification schemes are refined by MSMR’s editorial staff. The major classification system for diagnoses, ICD-10-CM, features over 68,000 separate codes.⁵ While the ICD-10-CM is organized in logical chapters, the groupings are not optimal for describing burdens of disease in a military population. Consequently, some re-groupings of diagnoses are necessary to achieve a meaningful portrayal of the burden in the military population.

The burden of disease in a young, healthy, predominantly male service member population will differ substantially from that of the general U.S. or global populations. Service applicants are medically screened prior to military service to ensure fitness requirements for physically demanding jobs, and throughout their service mandatory periodic (typically annual) health assessments and screenings among ACSMs may detect conditions potentially undetected in other populations. The numerous readiness-related outpatient visits required for each ACSM, the prescribed circumstances of military living, training requirements, and access to medical care without cost may contribute to different morbidity burden profiles compared to other population groups.

Individuals enlist or are commissioned into the active component typically between the ages of 17 and 25, with almost all members ending service by age 50. In 2022, the mean age of ACSMs in the U.S. Armed Forces was approximately 29, with 1.3% of the population over 50.³ By contrast, the median age of the U.S. population in 2022 was 38.9, with 36.1% over age 50.⁴ Women constituted 19.2% of the active component in 2023, compared to 51.0% in the general U.S. population.⁶

Within the military population and its specific environment, categories of illnesses and injuries requiring hospitalization have historically differed from those that result in the most outpatient visits. The added requirements for readiness are likely a major factor in outpatient health care provision, but rarely for hospitalization. The categories of medical conditions and readiness requirements that account for the most medical encounters overall may differ from those that affect the most individuals or have the most debilitating or long-lasting effects.⁴

This annual summary uses several health care burden measures to quantify the impacts in 2023 of various illnesses and injuries among members of the active component of the U.S. Armed Forces. Health care burden metrics include the total number of medical encounters, individuals affected, and hospital bed days. A consistent and comparative description of the burden of diseases and injuries, and subpopulations affected, is an important input to health decision-making and planning processes and can provide valuable information for where changes in policy or preventive emphasis may improve the medical readiness of the force.⁷

Methods

The population for this analysis includes all individuals who served in the active component of the Army, Navy, Air Force, Marine Corps, or Space Force at any time during the surveillance period of January 1, 2023 through December 31, 2023. Each service member contributed encounters and person-time only for the actual months served during the surveillance period. All data in this analysis were derived from records maintained in the Defense Medical Surveillance System, which documents both ambulatory care encounters and hospitalizations of active component members of the U.S. Armed Forces. DMSS contains all encounters in military medical and civilian treatment facilities when reimbursed through the MHS. Encounters not routinely and completely documented within fixed military and non-military hospitals and medical clinics (e.g., during deployments, field training exercises, or at sea) are excluded from this analysis.

DMSS data for all inpatient and outpatient medical encounters of ACSMs during the surveillance period were summarized according to the primary (first-listed) diagnosis if reported with an ICD-10 code between A00 and T88, an ICD-10 code beginning with Z37 (outcome of delivery), or Department of Defense unique personal history codes DOD0101–DOD0105 (personal history of traumatic brain injury). All illness- and injury-specific diagnoses, as defined by ICD-10 codes, were grouped into 25 burden of disease-related ‘categories’ and 153 ‘conditions’, which are described as major category conditions in this report, based on a modified version of the classification system developed for the GBD Study.⁴ This classification system was developed by the MSMR editorial staff in 2001 and is updated annually.

The GBD system groups diagnoses with common pathophysiologic or etiologic bases or significant DOD health policy importance. In this article, some diagnoses grouped into single categories in the GBD system (e.g., mental health disorders) were disaggregated to increase military relevance. In addition, injuries are classified by affected anatomic site rather than cause, as external causes of injuries using NATO Standardization Agreement (STANAG) 2050 codes are incompletely reported in military outpatient records.⁸

The morbidity burdens attributable to various conditions were estimated based on the total number of medical encounters associated with each condition, i.e., total hospitalizations and ambulatory visits for the condition with a limit of one encounter for an individual per condition each day; and numbers of service members affected by each condition, i.e., individuals with at least one medical encounter for the condition during the year; as well as total bed days during hospitalizations for each condition.

Results

Morbidity burden, by category

Provisional data indicate that affected ACSMs (n=584,756) experienced medical encounters due to injury more than any other morbidity-related category in 2023 (Figure 1a). Ranking third in terms of hospital bed days, this major burden of disease category accounted for about one-fourth (23.2%) of all medical encounters (Figure 1b). The injury category combines ICD-10 S (injury) and T codes (burns and poisonings); however, injuries account for nearly 98% of ambulatory encounters within the category (data not shown).

Mental health disorders accounted for more hospital bed days (n=213,905) than any other morbidity-related category, contributing over half (54.8%) of all hospital bed days, ranking fifth for individuals affected (Figures 1a and 1b). Together, injury and mental health disorders accounted for over two-thirds (64.8%) of all hospital bed days and 42.3% of all medical encounters.

Maternal conditions (e.g., pregnancy complications and delivery) accounted for a relatively large proportion of all hospital bed days (n=56,122; 14.4%) but a much smaller proportion of medical encounters overall (n=205,381; 1.5%) (Figures 1a and 1b). As women comprised only 19.2% of the active duty force in 2023, these summary statistics understate the impact of these conditions among that group. Maternal conditions were the most frequent category among women in the active component.

Medical encounters, by condition

In 2023, five burden of disease-related conditions accounted for almost one-third (33.2%) of all illness- and injury-related medical encounters: other back problems (e.g., lower back pain, other dorsalgia), organic sleep disorders (e.g., insomnia, obstructive sleep apnea), all other signs and symptoms (e.g., fever, headache, general signs and symptoms not otherwise specified), knee injuries, and arm/shoulder injuries (Figure 2). Moreover, the 10 conditions associated with the most medical encounters constituted more than half (56.6%) of all illness- and injury-related medical encounters.

The health conditions that accounted for the most medical encounters among ACSMs in 2023 were predominantly injuries, mental health disorders, and musculoskeletal diseases. Of reported injuries, knee (6.3%), arm/shoulder (6.0%), foot/ankle (3.8%), and leg (3.2%) resulted in the most medical encounters (Figure 2 and Table). Mental health disorder diagnoses resulted most frequently from anxiety (5.7%), adjustment (4.3%), mood (4.3%), and substance abuse disorders (2.8%). Other back problems (9.3%), all other musculoskeletal diseases (5.7%; e.g., pain in foot, pain in leg), and cervicalgia (1.8%) generated the most medical encounters from musculoskeletal diseases. COVID-19 accounted for 0.3% of total medical encounters, ranking 44th in 2023, continuing the decrease to 1.4% of total encounters seen in 2022.

Individuals affected, by condition

In 2023, the 10 conditions that affected the most service members were signs, symptoms, and other ill-defined conditions (all other signs and symptoms and respiratory/chest); musculoskeletal diseases (other back problems and all other musculoskeletal diseases); respiratory infections (upper respiratory infections); neurological conditions (organic sleep disorders); respiratory and chest, sense organ diseases (refraction/accommodation); injuries (knee and arm/shoulder); and skin diseases (all other skin diseases). COVID-19 affected 32,508 service members and ranked thirty-fifth for numbers affected, a considerable decrease in rank from twelfth in 2022.

Hospital bed days, by condition

Mood and substance abuse disorders accounted for nearly one-third (32.9%) of all hospital bed days (Figure 3) in 2023. Four mental health disorders (mood, substance abuse, adjustment, anxiety) and two maternal conditions (pregnancy complications, delivery) together accounted for almost two-thirds (63.5%) of all hospital bed days (Table and Figure 3). About 10% of all hospital bed days were attributable to injuries and poisonings. COVID-19 accounted for 0.11% of total hospital bed days among ACSMs, down from 0.3% in 2022 (Table).

Relationships between health care burden indicators

There was a strong positive correlation between numbers of medical encounters attributable to various conditions and numbers of individuals affected by those conditions (r=0.87) (data not shown). The three leading causes of medical encounters were among the five conditions that affected the most individuals (Table), while weak-to-moderate positive relationships were detected for hospital bed days attributable to conditions and numbers of individuals affected (r=0.22) by, or medical encounters associated (r=0.41) with, those conditions. For example, substance abuse disorders and labor and delivery were among the top-ranking conditions, by proportion of total bed days, but these conditions affected relatively few ACSMs in 2023.

Discussion

This MSMR report provides the most recent data available for a major disease matrix comparable to previous reports. Compared to 2022, overall major category conditions reported in 2023 increased by 16.9%, medical encounters increased by 18%, as well as individuals affected (8.6%) and hospital bed days (5.7%). This result is consistent with the major findings of prior MSMR reports on morbidity and health care burdens among U.S. military members.

Injuries, mental health disorders, and musculoskeletal disorders were the medical conditions in 2023 associated with the most medical encounters, highest numbers of affected service members, and greatest numbers of hospital days. Only 9 of the 153 burden of disease conditions comprising this report, or 5.8% of the listed conditions, accounted for slightly more than half of all illness- and injury-related medical encounters: two anatomic site-defined injuries (knee and arm/shoulder), three mental health disorders (anxiety, adjustment, and mood disorders), organic sleep disorders, two musculoskeletal conditions (other back problems and all other musculoskeletal diseases), and all other signs and symptoms.

Injuries were the single leading cause of death, disability, hospitalization, outpatient visits, and manpower loss among U.S. military service members in 2023.⁹

The pattern of illness and injury among U.S. active component members is distinct from other population groups with different demographic distributions and occupational hazards, such as the general U.S. population and non-service member MHS beneficiaries. Injuries, mental health disorders, and musculoskeletal conditions are identified in the literature as the leading causes of morbidity and disability among service members throughout military history, affecting readiness and health care provision.^9-11

Due to lifestyles that can be influenced by operational conditions, multiple combat missions, separation from family, among other factors, a number of mental disorders including occupational stress, depression, and suicide are common among military personnel.¹⁰ Some studies have reported significant associations between major depressive disorder and deployment.¹¹ Exposure to intense physical demands in training and operational environments increases risk of musculoskeletal injury, which contributes to significant morbidity among military personnel.¹² With psychosocial factors shown to be implicated in increased risk of developing back pain, approaching this and related issues holistically, rather than divided among discrete categories, would be beneficial.^13,14 Holistic, integrated approaches to care that not only reflect the identified burden of conditions and associated risk factors, foremost the unique health challenges that result from the unique complexities of service experience and the nature of combat, but which also consider the interplay between military and civilian health care systems would better meet the health needs of military personnel and veterans.¹⁵

Because an understanding of the associations between preventive health care and disease occurrence is required for prevention of injury and disease among service members, a comprehensive medical surveillance system is necessary for routine injury and disease monitoring and data-informed prioritization of research and successful prevention programs. These surveillance, analysis, and reporting efforts can culminate in effective partnerships between commanders, policy-makers, and service members for direct actions to prevent disease and injuries.^8,11 Reporting on the burden of disease and injury includes reliable quantification of their physical and psychosocial health impacts, as well as risk factors, that can provide valuable information about the health status of a population, allowing optimal resource allocation for prevention and treatment. An accurate estimate of the health status of the armed forces can be used not only for determining expected health care use and costs and the prioritization of effective interventions, but evaluations of their impacts and cost-effectiveness.¹⁶ Recent and accurate information on the scale of health disorders among service members, groups noticeably at risk, and trends in their health statuses over time are critical data for policy-makers.

References

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