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Special Report: Prevalence of Selected Underlying Health Conditions Among Active Component Army Service Members with Coronavirus Disease 2019, 11 February–6 April 2020

Image of 09 and 10_USS Comfort_Navy website. The hospital ship USNS Comfort returns to its homeport after treating patients in New York and New Jersey in support of the COVID-19 pandemic. (U.S. Navy photo by Mass Communication Specialist 1st Class Joshua D. Sheppard/Releaseds)


The burden of COVID-19 in the Army AC population is being evaluated through active and passive surveillance daily; however, a summary of the prevalence of comorbidities in confirmed COVID-19 cases in the Army AC has not yet been published. The most common comorbidities in Army service members hospitalized for COVID-19 were history of obesity, hypertension, obstructive sleep apnea, and neurologic conditions.


COVID-19 is a highly infectious and potentially serious respiratory illness that can lead to hospitalization or death. Individuals with pre-existing medical conditions should exercise extreme caution to prevent this illness.


The novel coronavirus (severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) is exhibiting widespread community transmission throughout most of the world. Previous reports have evaluated the risk of serious illness in civilians diagnosed with COVID-19; however, similar reports have not been compiled for the Army active component (AC) population. COVID-19 has been a reportable condition for the Department of Defense since 5 February 2020, and, as of the morning of 6 April, a total of 873 cases were reported to the Disease Reporting System internet from Army installations. Of these cases, a total of 219 (25.1%) were identified as Army AC service members. The majority of these cases did not require hospitalization (n=207; 94.5%). The most common comorbidities present in nonhospitalized cases included other chronic illnesses (43.5%), neurologic disorders (24.6%), and obesity (21.7%). Overall, 12 cases (5.5%) required hospitalization. Hospitalized cases had a history of obesity (58.3%), neurologic disorder (50.0%), other chronic illnesses (41.7%), and hypertension (25.0%). No comorbidities were present among 27.1% (n=56) of nonhospitalized cases and 25.0% (n=3) of hospitalized cases.


In early January 2020, the China Centers for Disease Control announced they had identified a novel coronavirus (severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2) as the cause of a cluster of viral pneumonia of previously unknown etiology in Wuhan, China. As more countries continued to report widespread community transmission, the World Health Organization (WHO) declared a pandemic of coronavirus disease 2019 (COVID-19) on 11 March 2020. As of 8 April 2020, over 1.35 million cases and over 79,000 deaths had been reported by WHO.1 As of the morning of 6 April 2020, a total of 873 cases of COVID-19 had been reported to the Disease Reporting System internet (DRSi) from Army installations and some joint installations; the case counts include all cases reported from these installations, regardless of service, patient, or beneficiary status.2 The majority of cases were not hospitalized (n=773; 88.5%); 96 cases (11.0%) were hospitalized for this illness and 4 died (0.4%) (data not shown). Of the reported cases, a total of 328 (37.6%) were identified as active component (AC) service members from any military service (data not shown).

Several preliminary reports have summarized the epidemiology and clinical characteristics of COVID-19 patients.3–8 The SARS-CoV-2 virus is highly infectious and appears to have more negative impacts on patients 60 years or older than on adults under 40 years old or children.2,3,5,9–11 Several underlying health conditions are thought to increase the risk of severe illness, including pre-existing conditions such as immunocompromised status, history of cancer, cardiovascular disease, and diabetes mellitus.The U.S. Centers for Disease Control and Prevention (CDC) COVID-19 Response Team examined these conditions and other select underlying health conditions among the first 122,653 reported cases in the U.S. and concluded that persons with underlying health conditions such as diabetes mellitus, chronic lung disease, or cardiovascular disease had a higher risk for severe COVID-19–associated disease than those without these conditions.9

Service members in the U.S. Army have to meet occupational health and fitness standards in order to continue their careers in the Armed Forces. As such, compared to the general U.S. population, service members are typically characterized as younger, more physically fit, and with lower rates of chronic disease; this is sometimes referred to the healthy soldier effect. However, a study of cardiovascular disease comparing 2012 Periodic Health Assessment data to data from the 2011–2012 National Health and Nutrition Examination Survey noted that service members had an increased prevalence of elevated blood pressure and had a similar prevalence of body mass index in the overweight and obese ranges compared to the general population.12 Periodic reports by the U.S. Army Public Health Center (APHC) echo these findings for the prevalence of certain chronic diseases among AC Army members.13 For example, in 2018, among the AC service members evaluated in the APHC reports, 19% had 1 or more diagnosed chronic conditions13 and prevalence ranged from 13% to 37% across Army installations. Arthritis (9.3%) was the most common of the conditions assessed, followed by cardiovascular conditions (6.0%) and hypertension (5.6%).13 Additionally, 17% of service members were classified as obese during Army physical fitness tests, with the prevalence of obesity ranging from 11% to 25% across Army installations.13

This report provides preliminary information on the prevalence of select underlying conditions among confirmed cases of COVID-19 among U.S. Army AC service members. Of interest was the distribution of these conditions by hospitalization status and age. Causal relationships were not explored.


Study population

All confirmed cases of COVID-19 reported to the DRSi from 11 February 2020 through 6 April 2020 by 0500 EDT were evaluated for this report. Per Department of Defense (DoD) Office of the Under Secretary of Defense memorandum “Force Health Protection Guidance for the Novel Coronavirus Outbreak,” all cases of COVID-19 must be reported to the DRSi.14 The DRSi is a passive surveillance system for selected diseases identified as reportable medical events and has served as the main system of record for surveillance of all cases of COVID-19 in the Army population. Identities of cases were confirmed by patient identifiers (e.g., social security number) for an existing electronic medical record. To confirm that all reported cases were valid cases, the laboratory and encounter sections of all case patients’ medical records were searched for a report of a positive COVID-19 laboratory result.

Throughout the study period, confirmed cases of COVID-19 included all patients with positive or presumptive positive laboratory results. At the time of this study, the only laboratory tests performed within the Military Health System (MHS) and civilian hospitals were SARS-CoV-2 polymerase chain reaction tests. All confirmed cases among Army AC service members reported to the DRSi from 11 February 2020 through 6 April 2020 (by 0500 EDT) from any military treatment facility (MTF) were included in the analysis. A COVID-19 reporting page was not available in the DRSi until 11 February 2020. Until this time, a temporary reporting page was used; however, no confirmed cases of COVID-19 were reported in the Army AC service member population before 11 February 2020. National Guard members and Army Reserve active duty members, dependents, and retirees were excluded from the analysis, as reportable medical events among these groups are not as reliably reported to the DRSi because of differences in procedural policies. Because the processes for validating cases of COVID-19 reported to the DRSi differ between the Army, Air Force, Navy, and Marine Corps, all cases among Air Force, Navy, and Marine Corps AC service members reported to the DRSi were also excluded from the analysis.

February 2020 population data for active duty Army soldiers were extracted by age group and sex from the Defense Enrollment Eligibility Reporting System population summary. This summary contains aggregate demographic information for service members, civilians, and their eligible family members. These data were extracted using the MHS Management Analysis and Reporting Tool.

Study design

All COVID-19 patients meeting the case definition during the study period were identified, and their healthcare histories were searched for the underlying health conditions under consideration. Medical record reviews were performed using the Armed Forces Health Longitudinal Technology Application (AHLTA) electronic medical records system. AHLTA is the global electronic health record system used by the DoD. Each case’s medical records include a listing of all past diagnoses. These lists for each case were examined by epidemiologists for the select underlying conditions of interest.

The same list of underlying health conditions considered in the CDC COVID-19 Response Team report was used in this analysis.9 In brief, these include chronic lung disease (i.e., asthma, chronic obstructive pulmonary disease, and emphysema), cardiovascular disease, chronic renal disease, cancer or history of cancer, diabetes, current pregnancy, current or former smoking, liver disease, and neurologic disorder. The “neurologic disorder, neurodevelopmental, intellectual disability” category in the CDC report included headache/migraine. For the current study, cases with a diagnosis history of headaches were counted as having a neurologic disorder if they also had a diagnosis history of migraine or a concurrent history of a diagnosed head injury, such as traumatic brain injury. The other neurologic conditions included in the CDC report (i.e., dementia, memory loss or Alzheimer disease, seizure disorder, stroke, autism, aneurysm, multiple sclerosis, neuropathy, hereditary spastic paraplegia, myasthenia gravis, intracranial hemorrhage, and altered mental status) were also included in the current analysis. Some common conditions found in the study population, such as obesity and hypertension, were analyzed separately. The CDC report also included the overarching category “other chronic disease.” This category included thyroid disease, gastrointestinal disorder, hyperlipidemia, rheumatologic disorder, hematologic disorder, arthritis, mental health condition, urologic disorder, cerebrovascular disease, obstructive sleep apnea, fibromyalgia, gynecologic disorder, pulmonary or venous embolism, ophthalmic disorder, hypertriglyceridemia, endocrine disorder, substance abuse disorder, dermatologic disorder, and genetic disorder.

Analyses were conducted using Microsoft Excel 2013 (Microsoft Corporation, Redmond, WA) and SAS/STAT software, version 9.4 (2014, SAS Institute, Cary, NC). The frequencies of underlying health conditions were calculated for AC service members by hospitalization status (nonhospitalized vs. hospitalized), sex, and age group. No statistical comparisons were performed in this analysis.


A total of 219 AC service member case patients were identified with COVID-19 symptom onset dates ranging from 17 February to 2 April (Figure 1). The vast majority of cases did not require hospitalization (n=207; 94.5%). Although four-fifths of cases were males (n=175; 79.9%), the overall incidence rate of COVID-19 infection was higher among females (5.9 per 10,000 soldiers) than males (4.2 per 10,000 soldiers) (Table 1). The highest rate of COVID-19 infection was among the oldest (45 years or older) age group for both hospitalized cases (1.6 per 10,000 soldiers) and nonhospitalized cases (15.2 per 10,000 soldiers). The highest incidence rate of COVID-19 infection among males was among those 45 years or older (17.9 per 10,000 soldiers), while the highest incidence rate among females was among those aged 35–44 years (11.3 per 10,000 soldiers).

Medical record data for the 219 confirmed cases of COVID-19 were examined for 10 underlying conditions of interest (Table 2). About one-third of the total case patients (33.8%; n=74) had none of the selected comorbidities in their medical histories. Among the 207 COVID-19 patients who did not require hospitalization, 34.3% had no comorbidities (n=71). No case patients were pregnant or had a history of chronic liver disease. Among the 10 underlying conditions that were present, prevalence ranged from less than 1% (cardiovascular disease) to 43.4% (other chronic disease). The broad category “other chronic disease,” which included numerous diagnoses, was most prevalent among all case patients (n=95), followed by neurologic disorder (n=57; 26.0%) and obesity (n=52; 23.7%). Obstructive sleep apnea (n=42; 44.2%), hyperlipidemia (n=39; 41.1%), and mental health conditions (n=51; 53.7%) were the most common “other chronic diseases” for all case patients.

In comparing the distribution of underlying conditions among hospitalized and nonhospitalized confirmed cases, the small number of hospitalized cases precluded definitive conclusions about differences between the 2 groups.

Of the 12 (5.5%) case patients who were hospitalized, 4 (33.3%) were admitted to an intensive care unit (ICU) (Table 3). None of the hospitalized cases, including those that were admitted to the ICU, required a ventilator. The underlying conditions with the highest prevalence among hospitalized COVID-19 patients included hypertension (25.0%), obesity (58.3%), and neurologic disorder (50.0%) (Table 2). All 4 of the patients who were admitted to an ICU had 3 or more underlying conditions present (Table 3). In contrast, of the 8 patients who were hospitalized without admission to an ICU, 2 (25.0%) had 3 or more underlying conditions present and 3 (37.5%) had no underlying conditions present. Of the 207 COVID-19 cases who were not hospitalized, 32 (15.5%) had 3 or more underlying conditions (Table 3).


Because the nature of the population for this report differs from the CDC COVID-19 Response Team’s civilian population, direct comparisons are not possible. The patient population for this preliminary report is significantly smaller than the population described in the CDC report. In addition, the Army AC service member population does not include soldiers with underlying health conditions that would disqualify service members from enlistment in the Army, such as Alzheimer disease, Parkinson disease, intellectual disability, and others. On the other hand, conditions like hypertension, obesity, and neurologic disorders were observed often in soldiers. Diabetes mellitus was a significant underlying factor in the CDC report, with 10.9% of cases having this condition,9 whereas only 2.7% of the Army study population had this disease (including prediabetes). Finally, the neurologic disorder category was associated with just 0.7% of case patients in the CDC’s report,9 whereas 26.0% of Army patients had some history of neurologic disorder; many had a history of diagnosed migraines (n=28) and/or traumatic brain injury (n=21) (Table 2).

Because obesity was a common underlying condition for both hospitalized and nonhospitalized Army cases—the prevalence of obesity was 17% in the Army AC service member population in 2018—this condition may be a prominent risk factor for more severe COVID-19 infection in this particular population.13 While the highest rates of COVID-19 occurred among service members aged 45 years or older (16.8 per 10,000 soldiers), the Army study population was on average younger (mean=34.6 years) than the age groups that are considered most at risk for serious illness due to COVID-19. This age difference may be a major contributing factor to why only 5.5% of Army case patients required hospitalization for this illness compared to 8.5% of case patients in the CDC report (of 74,439 total cases with a completed case report form, 5,285 were hospitalized without ICU admission and 1,069 were hospitalized with ICU admission).9 It is also notable that the rate of nonhospitalized COVID-19 infection was higher among female compared to male service members (5.8 vs. 4.0 per 10,000 soldiers, respectively). The rate of hospitalized COVID-19 infection was lower among female cases compared to male cases (0.1 vs. 0.3 per 10,000 soldiers, respectively); however, the low case count of hospitalized female service members precludes making generalizations about the influence of sex on hospitalization rates among Army AC service members.

This report included several important limitations. First, this visual scan of underlying conditions, although thorough and performed by experienced epidemiologists, may not have captured all underlying conditions of interest. Although most Army AC service members receive medical care through the MHS, some conditions diagnosed by providers outside of the MHS may not have been captured in the AHLTA electronic medical record. Regardless, all case patients had diagnosis histories available to review in the MHS, and all of the underlying health conditions of interest diagnosed by MHS providers were captured by reviewing electronic medical records for each patient.

Secondly, although the DRSi is the main system of record for surveillance of all cases of COVID-19 in the DoD, there are gaps in this reporting system that are well known.15 It is likely that the DRSi does not capture all confirmed cases of COVID-19; however, several mitigating procedures were put into practice early on in the pandemic. COVID-19 surveillance training was provided to all DRSi reporters on 25 February 2020 in anticipation of an increase in the incidence of COVID-19 in the DoD population. Additionally, the Defense Health Agency (DHA) Army Satellite COVID-19 Surveillance Team has provided weekly training to Army personnel who have been assigned to report cases to the DRSi since mid-March 2020. The DHA Army Satellite COVID-19 Surveillance Team has also been collecting MHS laboratory data for all confirmed cases and contacting MTFs that have not yet reported cases as identified in the laboratory data. These efforts have led to a considerable increase in the usage of the DRSi for reporting COVID-19 cases, and MTFs have generally reported all known cases of COVID-19 as captured in other data sources to the DRSi within 24 hours of the diagnosis, per Army policy.

Finally, only the more serious cases that require diagnosis from a provider and laboratory confirmation are being captured in this surveillance study. Asymptomatic patients and those with mild illness that did not seek treatment would not be captured in this surveillance system; therefore, selection bias exists. The overall prevalence of COVID-19 is not yet well understood, including within the Army population.

All Army AC service members that are experiencing symptoms of COVID-19, including fever, cough, shortness of breath, or other symptoms should immediately contact their healthcare providers. Many Army installations have implemented higher health protection condition levels as their population sees widespread community transmission of COVID-19; the DHA Army Satellite COVID-19 Surveillance Team, in collaboration with the APHC COVID-19 Taskforce, is evaluating the impact of these strategies on the burden of COVID-19 at each installation.

Acknowledgments: The authors would like to thank the diligent work of the Army public health nurses, epidemiology technicians, and other public health professionals who have worked tirelessly in response to this pandemic.


1. World Health Organization. COVID-19 Dashboard. Accessed 6 April 2020.

2. Department of Defense. Defense Health Agency. Memorandum for Military Treatment Facility (MTF) Directors. Interim Guidance for MTF Director in Regards to 2019-Novel Coronavirus. 5 February 2020.

3. Chang D, Lin M, Wei L, et al. Epidemiologic and clinical characteristics of novel coronavirus infections involving 13 patients outside Wuhan, China [published online ahead of print 7 February 2020]. JAMA.

4. Kimball A, Hatfield KM, Arons M, et al. Asymptomatic and presymptomatic SARS-CoV-2 infections in residents of a long-term care skilled nursing facility—King County, Washington, March 2020. MMWR Morb Mortal Wkly Rep. 2020;69(13):377–381.

5. The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team. The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19)—China, 2020. CCDC Weekly. 2020;2:113–122.

6. Rothe C, Schunk M, Sothmann P, et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. N Engl J Med. 2020;382(10):970–971.

7. Holshue ML, DeBolt C, Lindquist S, et al. First case of 2019 novel coronavirus in the United States. N Engl J Med. 2020;382(10):929–936.

8. Liu YC, Liao CH, Chang CF, Chou CC, Lin YR. A locally transmitted case of SARS-CoV-2 infection in Taiwan. N Engl J Med. 2020; 382(11):1070–1072.

9. Centers for Disease Control and Prevention. Preliminary estimates of the prevalence of selected underlying health conditions among patients with coronavirus disease 2019—United States, February 12–March 28, 2020. MMWR Morb Mortal Wkly Rep. 2020;69:382–386.

10. Cai J, Xu J, Lin D, et al. A case series of children with 2019 novel coronavirus infection: clinical and epidemiological features [published online ahead of print 28 February 2020]. Clin Infect Dis.

11. Ong SWX, Tan YK, Chia PY, et al. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient [published online ahead of print 4 March 2020]. JAMA.

12. Shrestha A, Ho TE, Vie LL, et al. Comparison of cardiovascular health between US Army and civilians. J Am Heart Assoc. 2019;8(12):e009056.

13. U.S. Army Public Health Center. 2019 Health of the Force. Accessed 15 May 2020.

14. Office of the Under Secretary of Defense. Memorandum for Secretaries of the Military Departments. Force Health Protection Guidance for the Novel Coronavirus Outbreak. 30 January 2020.

15. Ambrose JF, Kebisek J, Gibson KJ, White DW, O’Donnell FL. Commentary: Gaps in reportable medical event surveillance across the Department of the Army and recommended training tools to improve surveillance practices. MSMR. 2019;26(8):17–21.

FIGURE 1. Hospitalized and nonhospitalized COVID-19 cases by onset date, active component, U.S. Army, 11 February–6 April 2020TABLE 1. Cases and incidence rates of COVID-19 by sex and age group, active component, U.S. Army, 11 February–6 April 2020
TABLE 2. Underlying health conditions among COVID-19 cases by hospitalization status, active component, U.S. Army, 11 February–6 April 2020
TABLE 3. Counts of underlying conditions by hospitalization status, active component, U.S. Army, 11 February–6 April 2020

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Last Updated: July 30, 2020
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