What Are the New Findings?

The hospitalization rate in 2020 was 47.1 per 1,000 person-years, the lowest rate of the most recent 10 years, during which period annual rates steadily declined. As in prior years, the majority (70.9%) of hospitalizations were associated with diagnoses in the categories of mental health disorders, pregnancy-related conditions, injury/poisoning, and digestive system disorders.

What Is the Impact on Readiness and Force Health Protection?

Not only are mental health disorders the most common diagnoses associated with hospitalizations, they are associated with the longest median hospital stay (6 days). Moreover, 5% of hospitalizations for mental health disorders had durations of stay greater than 30 days. Prolonged hospitalizations, subsequent aftercare, and early attrition because of such common disorders can have a negative impact on individual and unit operational readiness.

Background

This report documents the frequencies, rates, trends, and distributions of hospitalizations of active component members of the U.S. Army, Navy, Air Force, and Marine Corps during calendar year 2020. Summaries are based on standardized records of hospitalizations at U.S. military and non-military (reimbursed care) medical facilities worldwide. For this report, primary (first-listed) discharge diagnoses are considered indicative of the primary reasons for hospitalizations; summaries are based on the first 3 digits of the International Classification of Diseases, 10th Revision, used to report primary discharge diagnoses. Hospitalizations not routinely documented with standardized, automated records (e.g., during field training exercises or while shipboard) are not centrally available for health surveillance purposes and thus are not included in this report.

Frequencies, rates, and trends

In 2020, there were 62,459 records of hospitalizations of active component members of the U.S. Army, Navy, Air Force, and Marine Corps (Table 1); 33.7% of the hospitalizations were in non-military facilities (data not shown). The annual hospitalization rate (all causes) for 2020 was 47.1 per 1,000 service member person-years (p-yrs). This rate was the lowest of the years covered in this report (2011–2020), during which rates fell steadily each year until 2019 when the rate (52.2 per 1,000 p-yrs) exceeded that of 2018 (51.0 per 1,000 p-yrs) (Figure 1).

Hospitalizations, by illness and injury categories

In 2020, 4 diagnostic categories accounted for 70.9% of all hospitalizations of active component members: mental health disorders (28.7%), pregnancy- and delivery-related conditions (25.1%), injury/poisoning (8.8%), and digestive system disorders (8.3%) (Table 1). Similar to 2016 and 2018, in 2020 there were more hospitalizations for mental health disorders than for any other major diagnostic category (per ICD-10); 2009 was the last year in which the number of hospitalizations for pregnancy- and delivery-related conditions exceeded the number for mental health disorders (data not shown).

Comparing 2020 to 2016, numbers of hospitalizations decreased in all major categories of illnesses and injuries except for mental health disorders, pregnancy and delivery, and hematologic and immune disorders, which increased 7.2%, 1.1%, and 9.2%, respectively (Table 1). The largest drop in the number of hospitalizations during 2016–2020 was seen in the category of "musculoskeletal system and connective system disorders" hospitalization difference, 2016–2020: -2,081; 34.7% decrease).

Hospitalizations, by sex

In 2020, the hospitalization rate (all causes) among females was more than 3 times that of males (114.8 per 1,000 p-yrs vs. 32.6 per 1,000 p-yrs, respectively). Excluding pregnancy and delivery, the rate of hospitalizations among females (46.1 per 1,000 p-yrs) was 41.6% higher than among males (data not shown).

Overall hospitalization rates were higher (i.e., the rate difference [RD] was greater than 1.0 per 1,000 p-yrs) among females than males for mental health disorders (female:male, RD: 7.4 per 1,000 p-yrs); genitourinary disorders (RD: 2.9 per 1,000 p-yrs); and neoplasms (RD: 1.4 per 1,000 p-yrs) (data not shown). With the exception of pregnancy- and delivery-related conditions, hospitalization rates were similar among males and females for the remaining 13 major disease-specific categories (data not shown).

Relationships between age and hospitalization rates varied considerably across illness- and injury-specific categories. For example, among both males and females, hospitalization rates generally increased with age for musculoskeletal system/connective tissue disorders, neoplasms, and circulatory, genitourinary, digestive, nervous, and endocrine/nutrition/immunity disorders (Figure 2). Among service members aged 30 years or older, there was a pronounced difference by sex in the slopes of the rates of neoplasms, with the rates among females notably higher than among males in the same age groups. Rates decreased with age for mental health disorders but were relatively stable across age groups for injury/poisoning, signs/symptoms/ill-defined conditions, and infectious/parasitic diseases.

Most frequent diagnoses

In 2020, adjustment disorder was the most frequent discharge diagnosis among males (n=4,433) (Table 2). Alcohol dependence (n=2,303), acute appendicitis (n=1,197), major depressive disorder [recurrent, severe without psychotic features] (n=1,104), major depressive disorder [single episode, unspecified] (n=1,087), other symptoms and signs involving emotional state (n=542), and post-traumatic stress disorder (PTSD) (n=523) were the next 6 most frequent diagnoses in males (Table 2).

In 2020, the most frequent discharge diagnosis among females was adjustment disorder (n=1,352). Pregnancy- and delivery-related conditions represented the next 5 leading causes of hospitalizations among females, and this category alone accounted for 59.7% of all hospitalizations of females (Table 3). The top 5 discharge diagnoses in this condition category included post-term (late) pregnancy (n=1,332), abnormality in fetal heart rate and rhythm (n=922), maternal care due to uterine scar from previous surgery (n=856), premature rupture of membranes [onset of labor within 24 hours of rupture] (n=847), and first degree perineal laceration during delivery (n=793). After the top 6 discharge diagnoses described above for females, the other leading causes of hospitalizations among females were recurrent major depressive disorder without psychotic features (n=454), PTSD (n=448), major depressive disorder [single episode, unspecified] (n=380), and alcohol dependence (n=304). Combined, mental health disorder diagnoses accounted for one-sixth (17.1%) of all hospitalizations of females.

Injury/poisoning

As in the past, in 2020, injury/poisoning was the third leading cause of hospitalizations of U.S. military members (Table 1). Of all injury/poisoning-related hospitalizations in U.S. military medical facilities (n=3,326), more than half (63.4%) had a missing or invalid NATO Standardization Agreement (STANAG) code (Table 4). More than one-third (35.6%) of all "unintentional" injury/poisoning-related hospitalizations in U.S. military facilities (n=1,068) were considered caused by falls and miscellaneous (n=380), while land transport (n=236) accounted for 22.1% of "unintentional" injury/poisoning-related hospitalizations (Table 4). 

Among males, injury/poisoning-related hospitalizations were most often related to infection following a procedure, concussion, fracture of the tibial shaft, or fracture of the mandible (Table 2). Among females, injury/poisoning-related hospitalizations were most often related to poisoning by/adverse effect of acetaminophen derivatives, unspecified injury, infection following a procedure, concussion, or poisoning by/adverse effect of/under dosing of other and unspecified antidepressants (Table 3).

Durations of hospitalizations

During 2011–2020, the median duration of hospital stays (all causes) remained stable at 3 days (Figure 3). As in previous years, medians and ranges of durations of hospitalizations varied considerably across major diagnostic categories. For example, median lengths of hospitalizations varied from 2 days (e.g., musculoskeletal system disorders; genitourinary system disorders; signs, symptoms, and ill-defined conditions) to 6 days (mental health disorders). For most diagnostic categories, less than 5% of hospitalizations exceeded 12 days, but for 7 categories, 5% of hospitalizations had longer durations: circulatory system disorders (13 days), nervous system/sense organ disorders (14 days), infectious/parasitic diseases (15 days), injury/poisoning (21 days), neoplasms (26 days), other non-pregnancy-related factors influencing health status and contact with health services (primarily orthopedic aftercare and rehabilitation following a previous illness or injury) (30 days), and mental health disorders (30 days) (Figure 4). It is noteworthy that, for one specific infectious disease, COVID-19, although the median length of hospital stay was 5 days, 5% of patients had hospital stays of 18 days or longer.

Hospitalizations, by service

Among active component members of the Air Force, pregnancy- and delivery-related conditions accounted for more hospitalizations than any other category of illnesses or injuries; however, among active component members of the Army, Navy, and Marine Corps, mental health disorders were the leading cause of hospitalizations (Table 5). For the Navy, this was a change from the results for 2019, when pregnancy and delivery-related conditions were most numerous. The crude hospitalization rate for mental health disorders among active component Army members (15.2 per 1,000 p-yrs) was higher than among members of all other services.

Injury/poisoning was the third leading cause of hospitalizations in the Army and the Marine Corps, and fourth in the Navy and Air Force (Table 5). The hospitalization rate for injury/poisoning was highest among Army (5.6 per 1,000 p-yrs) and Marines Corps members (4.8 per 1,000 p-yrs) and lowest among Air Force members (2.6 per 1,000 p-yrs).

Editorial Comment

The hospitalization rate for all causes among active component members in 2020 was the lowest rate of the past 10 years. As in past years, in 2020, mental health disorders, pregnancy- and delivery-related conditions, and injury/poisoning accounted for more than half of all hospitalizations of active component members. Adjustment and mood disorders were among the leading causes of hospitalizations among both male and female service members. In recent years, attention at the highest levels of the U.S. military and significant resources have focused on detecting, diagnosing, and treating mental health disorders—especially those related to long and repeated deployments and combat stress. Annual crude rates of hospitalizations for mental health disorders increased between 2015 and 2017 and have remained relatively stable between 2017 and 2020. The annual number of mental health disorder-related hospitalizations has been approximately 18,000 since 2017. 

The reasons for the recent downturn in the trends for annual numbers of hospitalizations overall and for the slight increase in mental health disorder–related hospitalizations in particular are not clear. It is conceivable that there has been a decline in the impact of combat and peacekeeping operations on overall morbidity among service members since the withdrawal of U.S. forces from Iraq and the official end to combat operations in Afghanistan. The decrease in hospitalizations in 2020 may also have been a consequence of the COVID-19 pandemic, during which elective admissions to hospitals were discouraged and the public health measures of social distancing and use of personal protective equipment may have reduced the incidence of not only infectious diseases but also of injuries. Continued monitoring of hospitalizations and all other health care encounters over time may permit elucidation of the possible reasons for the recent trends in hospitalization. 

This summary has certain limitations that should be considered when interpreting the results. For example, the scope of this report is limited to members of the active components of the U.S. Armed Forces. Many reserve component members were hospitalized for illnesses and injuries while serving on active duty in 2020; however, these hospitalizations are not accounted for in this report. Please refer to the snapshot pertaining to the reserve component elsewhere in this issue of the MSMR. In addition, many injury/poisoning-related hospitalizations occur in non-military hospitals. If there are significant differences between the causes of injuries and poisonings that resulted in hospitalizations in U.S. military and non-military hospitals, the summary of external causes of injuries requiring hospital treatment reported here (Table 4) could be misleading. Also, this summary is based on primary (first-listed) discharge diagnoses only; however, in many hospitalized cases, there are multiple underlying conditions.

For example, military members who are wounded in combat or injured in motor vehicle accidents may have multiple injuries and complex medical and psychological complications. In such cases, only the first-listed discharge diagnosis would be accounted for in this report. Finally, it should be noted that medical data from sites that were using the new electronic health record for the Military Health System, MHS GENESIS, between July 2017 and Oct. 2019 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 data for individuals seeking care at any of these facilities from July 2017 through Oct. 2019 were not included in the current analysis. Even with these limitations, this report provides useful and informative insights regarding the natures, rates, and distributions of the most serious illnesses and injuries that affect active component military members.