What Are the New Findings?

In 2019, the average active component service member had about 13 ambulatory encounters. About 74% of illness- and injury-related encounters were for musculoskeletal system/connective tissue disorders, mental health disorders, nervous system/sense organ disorders, and signs/symptoms/ill-defined conditions. Rates for most illnesses and injuries tended to be higher among females than males.

What Is the Impact on Readiness and Force Health Protection?

Conditions affecting the musculoskeletal system (including injuries) and mental health disorders are common causes of ambulatory encounters among active component service members. These encounters themselves limit affected members' availability for duty. These conditions that affect readiness continue to warrant research and preventive measures to reduce their impact on the force.

Background

This report documents the frequencies, rates, trends, and characteristics of ambulatory health care visits of active component members of the U.S. Army, Navy, Air Force, and Marine Corps during 2019. Ambulatory visits of U.S. service members in fixed military and non-military (reimbursed through the Military Health System [MHS]) medical treatment facilities are documented with standardized, automated records. These records are routinely archived for health surveillance purposes in the Defense Medical Surveillance System (DMSS), which is the source of data for this report. Ambulatory visits that are not routinely and completely documented with standardized electronic records (e.g., during deployments, field training exercises, or at sea) are not included in this analysis. As in previous MSMR reports, all records of ambulatory visits of active component service members were categorized according to the first 4 characters of the International Classification of Diseases, 10th Revision (ICD-10) codes entered in the primary (first-listed) diagnostic position of the visit records.¹ The analysis depicts the distribution of diagnoses according to the 17 traditional categories of the ICD system.

Frequencies, rates, and trends

During 2019, there were 17,431,300 reported ambulatory visits of active component service members. The crude annual rate (all causes) was 13,255.3 visits per 1,000 person-years (p-yrs) or 13.3 visits per p-yr; thus, on average, each service member had approximately 13 ambulatory encounters during the year (Table 1). The rate of documented ambulatory visits in 2019 was 4.7% higher than the rate in 2018 (12,661.4 visits per 1,000 p-yrs) but 8.2% lower than the peak in 2012 (14,438.8 visits per 1,000 p-yrs) (Figure 1). In 2019, 30.9% of ambulatory visits were classified into the "other" category (i.e., other factors influencing health status and contact with health services, excluding pregnancy-related), which includes health care not related to a current illness or injury (Table 1). Such care includes routine and special medical examinations (e.g., periodic, occupational, or retirement), therapeutic and rehabilitative treatments for previously diagnosed illnesses or injuries (e.g., physical therapy), immunizations, counseling, deployment-related health assessments, and screening.

In 2019, there were 12,048,041 documented ambulatory visits for illnesses and injuries (ICD-10: A00–T88, including relevant pregnancy Z-codes), not including diagnoses classified as "other". for a crude annual rate of illness- and injury-related visits of approximately 9.2 visits per p-yr (Table 1). The rate of ambulatory visits for illnesses and injuries in 2019 was similar to the rate in 2017 (9.1 visits per p-yr) but slightly higher than the rate in 2015 (8.0 visits per p-yr).

Ambulatory visits, by diagnostic categories

In 2019, 4 major diagnostic categories accounted for almost three-quarters (73.7%) of all illness- and injury-related ambulatory visits among active component service members: musculoskeletal system/connective tissue disorders (36.7%); mental health disorders (16.2%); disorders of the nervous system and sense organs (11.3%); and signs, symptoms, and ill-defined conditions (9.6%) (Table 1).

Between 2015 and 2019, there were increases in the numbers of visits in 8 major diagnostic categories of illness and injury and decreases in 8 categories (Table 1). In terms of both the numbers of ambulatory visits and the percentage change in the numbers of visits for illnesses and injuries, the largest increases during 2015–2019 were for musculoskeletal system/connective tissue disorders (change: +1,204,311 visits; +37.5%) and disorders of the nervous system and sense organs (change: +304,882; +28.8%). The largest decrease in numbers of visits between 2015 and 2019 was for injury and poisoning (change: -39,049; -4.9%) (Table 1). The largest percentage decreases in ambulatory visits during 2015–2019 were for congenital anomalies (change: -5,811; -23.0%); endocrine, nutrition, and immunity disorders (change: 23,168; -19.9%); disorders of the circulatory system (change: -20,840; -14.6%); and infectious and parasitic diseases (change: -20,132; -9.5%); moreover, the rates of ambulatory visits for illnesses and injuries in 3 of these categories (congenital anomalies; endocrine, nutrition, and immunity disorders; and infectious and parasitic diseases) showed consistent decreases during the 5-year period (2015–2017 and 2017–2019).

In general, the relative distributions of ambulatory visits by ICD-10 diagnostic categories remained stable over the surveillance period (Table 1). In a comparison of the numbers and rates of visits attributable to each of the 17 major diagnostic categories in the years 2015 and 2019, the rank orders of 1 pair of categories were exchanged: hematologic and immune system disorders (17th to 16th) and congenital anomalies (16th to 17th). The rank orders of the 17 major diagnostic categories were the same in 2017 and 2019.

Ambulatory visits, by sex

In 2019, males accounted for nearly three-fourths (73.2%) of all illness- and injury-related visits; however, the annual crude rate among females (14.6 visits per p-yr) was 81.2% higher than that among males (8.1 visits per p-yr) (data not shown). Excluding pregnancy- and delivery-related visits (which accounted for 10.5% of all non-Z-coded ambulatory visits among females), the illness and injury ambulatory visit rate among females was 13.1 visits per p-yr. As in the past, rates for illness- and injury-related categories were generally higher among females than males (Figure 2).

Among all illness- and injury-specific diagnoses, 3 of the 5 diagnoses with the largest numbers of ambulatory visits were the same for males and females. However, the crude rate (per 1,000 p-yrs) was at least 41% higher among females than males for these 3 common diagnoses: pain in joint (female: 1,853.0; male: 1,254.3; female:male rate ratio [RR]: 1.48); low back pain (female: 791.9; male: 560.9; RR: 1.41); and adjustment disorders (female: 620.0; male: 266.3; RR: 2.33) (data not shown). Five other diagnoses were among the 10 most common diagnoses for both males and females: pain in limb, hand, foot, fingers, and toes; post-traumatic stress disorder (PTSD); sleep apnea; alcohol dependence; and cervicalgia. Of note, sleep apnea was the 3rd most frequent illness- or injury-specific primary diagnosis during ambulatory visits of males, but it ranked as the 9th most common diagnosis among females. Among females, the 7th most common diagnosis was anxiety disorder, unspecified, which was the 11th most common diagnosis among males (Tables 2, 3).

Across diagnostic categories, relationships between age group and ambulatory visit rates were broadly similar among males and females (Figure 2). For example, among both males and females, ambulatory visit rates for neoplasms and circulatory disorders among those aged 40 years or older were 15 or more times the rates among those younger than 20 years old; in contrast, clinic visit rates for infectious and parasitic diseases were lower among the oldest compared to the youngest service members. As in the past, ambulatory visit rates for disorders of the nervous system; digestive system; endocrine system, nutrition, and immunity; and musculoskeletal system/connective tissue rose more steeply with advancing age than most other categories of illness or injury (for which rates were relatively stable or only modestly increased) (Figure 2).

Dispositions after ambulatory visits

Because disposition codes are assigned to ambulatory medical encounters that occur only at military treatment facilities (MTFs), the following metrics do not include outsourced care. Approximately 61.7% of all illness- and injury-related visits resulted in "no limitation" (i.e., duty without limitations) dispositions (data not shown). Approximately 1 in 52 (1.9%) illness- and injury-related visits resulted in "convalescence in quarters" dispositions (data not shown). The illness- and injury-related diagnostic categories with the highest proportions of "limited duty" dispositions were injuries and poisonings (14.9%) and musculoskeletal system/connective tissue disorders (12.6%) (Figure 3). The illness- and injury-related diagnostic categories with the highest proportions of "convalescence in quarters" were infectious and parasitic diseases (14.4%) and diseases of the respiratory system (13.6%). Musculoskeletal system/connective tissue disorders (55.4%) accounted for more than one-half of all "limited duty" dispositions, and mental health disorders (15.4%) and injury/poisoning (11.3%) together accounted for more than one-quarter (26.8%) (Figure 4). Diseases of the respiratory system accounted for about three-eighths (37.8%) of all "convalescence in quarters" dispositions—more than twice as many (n=87,207) as any other disease category, except signs and symptoms (21.9%).

Editorial Comment

During the 5-year period, the distribution of illness- and injury-related ambulatory visits in relation to their reported primary causes has remained fairly stable. In 2019, musculoskeletal system/connective tissue and mental health disorders accounted for more than one-half (52.9%) of all illness- and injury-related diagnoses documented on standardized records of ambulatory encounters. Over the course of the surveillance period (2015–2017 and 2017–2019), 5 major illness- and injury-related categories (musculoskeletal system/connective tissue disorders; disorders of the nervous system and sense organs; hematologic and immune disorders; signs/symptoms and ill-defined conditions; and disorders of the respiratory system) showed consistent increases in numbers of ambulatory visits and rates and 3 major illness- and injury-related categories (endocrine, nutrition, and immunity disorders; infectious and parasitic diseases; and neoplasms) showed consistent decreases. The former upward trend is likely due, at least in part, to an increase in active duty military strength. At the end of Sept. 2019, there were approximately 25,000 more military personnel on active duty than at the same time in 2015.²

During 2015–2019, the relative ranking of injuries and poisonings (rank: 6) as a primary cause of ambulatory visits remained stable. However, the numbers and rates of visits declined by 3.5% and 5.8%, respectively, since 2017. Nevertheless, the potential military operational impacts of various conditions cannot be assessed by numbers of attributable ambulatory visits alone. For example, in 2019, injuries and poisonings accounted for approximately 1 of every 23 ambulatory visits overall; however, of ambulatory visits occurring at MTFs, 16.4% (slightly less than 1 in 6) had limited duty or "convalescence in quarters" dispositions. Of particular note, in relation to injuries and musculoskeletal conditions, in 2019, as in the past, joint and back injuries and other disorders accounted for large numbers of ambulatory visits; resources should continue to be focused on preventing, treating, and rehabilitating back pain and injuries among active component members.

It should be noted that the summary data using the major diagnostic categories of the ICD-10 system presented here deserve as detailed an examination as presented in Tables 2 and 3. For example, the general category identified as "nervous system" encompasses diseases of the nervous system and the sense organs (eyes and ears). Results presented in Tables 2 and 3 indicate that the more common diagnoses in this category refer to sleep disorders, disorders of refraction and accommodation, and pain disorders. Closer scrutiny reveals that the overall increase (n=304,882) in annual visits for this category from 2015 to 2019 (described earlier) can be attributed mostly to a rise in diagnoses of organic sleep disorders from 365,822 in 2015 to 563,981 in 2019.³

Several limitations should be considered when interpreting the findings of this report. For example, ambulatory care that is delivered by unit medics and at deployed medical treatment facilities (such as in Afghanistan or Iraq or at sea) may not be documented on standardized, automated records and thus not archived in the DMSS. In turn, this summary does not reflect the experience of active component military members overall to the extent that the natures and rates of illnesses and injuries may vary between those who are deployed and those who are not deployed.

In addition, this summary is based on primary (first-listed) diagnosis codes reported on ambulatory visit records. As a result, the current summary discounts morbidity related to comorbid and complicating conditions that may have been documented in secondary diagnostic positions of the health care records. Furthermore, the accuracy of reported diagnoses likely varies across conditions, care providers, treatment facilities, and clinical settings. Although some specific diagnoses made during individual encounters may not be definitive, final, or even correct, summaries of the frequencies, natures, and trends of ambulatory encounters among active component members are informative and potentially useful. For example, the relatively large numbers of ambulatory visits for mental health disorders in general and the large numbers of visits for organic sleep disorders among males reflect patterns of responses by the MHS to the effects of combat- and deployment-related stresses on active component service members.

Also, this report documents all ambulatory health care visits but does not provide estimates of the incidence rates of the diagnoses described. In contrast to common, self-limited, and minor illnesses and injuries that require very little, if any, follow-up or continuing care, illnesses and injuries that necessitate multiple ambulatory visits for evaluation, treatment, and rehabilitation are overrepresented in this summary of the ambulatory burden of health care. Finally, the new electronic health record for the MHS, MHS GENESIS, was implemented at 4 military treatment facilities in the state of Washington in 2017 (Naval Hospital Oak Harbor, Naval Hospital Bremerton, Air Force Medical Services Fairchild, and Madigan Army Medical Center). Implementation of the second wave of MHS GENESIS sites began in 2019 and included 3 facilities in California (Travis Air Force Base [AFB], the Presidio of Monterey, and Naval Air Station Lemoore) and 1 in Idaho (Mountain Home AFB). Medical data from facilities using MHS GENESIS are not available in the DMSS. Therefore, medical encounter data for individuals seeking care at any of these facilities after their conversion to MHS GENESIS were not included in the current analysis.

References

1. Armed Forces Health Surveillance Branch. Ambulatory visits, active component, U.S. Armed Forces, 2016. MSMR. 2017;24(4):16–22.
2. Defense Manpower Data Center. DOD personnel, workforce reports and publications. Active duty military personnel by service by rank/grade. Sept. 2019 and Sept. 2015. https://www.dmdc.osd.mil/appj/dwp/dwp_reports.jsp. Accessed 20 April 2020.
3. Armed Forces Health Surveillance Center. Ambulatory visits, active component, U.S. Armed Forces, 2015. MSMR. 2016;23(4):17–25.