Monitoring Exposure to Ebola and Health of U.S. Military Personnel Deployed in Support of Ebola Control Efforts — Liberia, October 25, 2014–February 27, 2015

Anthony P. Cardile, DO1; Clinton K. Murray, MD2; Christopher T. Littell, DO1; Neel J. Shah, MD1; Matthew N. Fandre, MD1; Dennis C. Drinkwater, MD1; Brian P. Markelz, MD1; Todd J. Vento, MD1,2 (Author affiliations at end of text)

In response to the unprecedented Ebola virus disease (Ebola) outbreak in West Africa, the U.S. government deployed approximately 2,500 military personnel to support the government of Liberia. Their primary missions were to construct Ebola treatment units (ETUs), train health care workers to staff ETUs, and provide laboratory testing capacity for Ebola. Service members were explicitly prohibited from engaging in activities that could result in close contact with an Ebola-infected patient or coming in contact with the remains of persons who had died from unknown causes. Military units performed twice-daily monitoring of temperature and review of exposures and symptoms ("unit monitoring") on all persons throughout deployment, exit screening at the time of departure from Liberia, and post-deployment monitoring for 21 days at segregated, controlled monitoring areas on U.S. military installations. A total of 32 persons developed a fever during deployment from October 25, 2014, through February 27, 2015; none had a known Ebola exposure or developed Ebola infection. Monitoring of all deployed service members revealed no Ebola exposures or infections. Given their activity restrictions and comprehensive monitoring while deployed to Liberia, U.S. military personnel constitute a unique population with a lower risk for Ebola exposure compared with those working in the country without such measures.

Background

The Ebola epidemic in West Africa has caused approximately 11,000 deaths in Sierra Leone, Liberia, and Guinea (January 5, 2014–May 27, 2015) (1). The U.S. military deployed approximately 2,500 service members to construct ETUs, conduct World Health Organization–based training of Liberian and international health care workers to staff the units, establish laboratories for Ebola testing, and deliver sustainable logistical ETU support.

CDC, the U.S. Department of Defense (DoD), and other agencies established exposure risk categories and clinical criteria to guide public health actions for potentially exposed or infected persons traveling from Ebola-affected countries (2–6). Risk categories for deployed DoD personnel differed from CDC categories for civilian populations (Table 1). From October 25, 2014, through February 27, 2015, the 101st Airborne Division (Air Assault) commanded military forces under Operation United Assistance. Monitoring and surveillance data from DoD personnel deployed to Liberia during this period were analyzed to evaluate the effectiveness of activity restrictions and unit monitoring in identifying potential Ebola exposures, and to describe the types of illnesses that occurred among deployed DoD personnel who developed fever.

DoD Disease Monitoring and Screening Procedures

U.S. military units in Liberia conducted unit monitoring twice daily on all deployed service members (2). Any person with a temperature ≥100.4°F (≥38.0°C), or any exposure or symptom concerns, was taken to the nearest DoD medical facility for evaluation by medical personnel. These personnel completed an Ebola risk assessment using a standard screening form (available at http://www.dtic.mil/whs/directives/forms/eforms/dd2990.pdf) (2). Service members' adherence with prescribed malaria chemoprophylaxis also was assessed as part of the daily unit monitoring program. At locations where U.S. military units were based, Liberian government employees screened temperatures of all entering persons at controlled access points. Non-U.S. personnel with fever were denied entry, and febrile U.S. personnel were referred for on-site medical evaluation. Service members were prohibited through military orders from providing medical care to local nationals, being in close proximity to or having physical contact with any person known to have Ebola, eating local food including "bush-meat," and having contact with the remains of persons who might have died from Ebola or whose cause of death was unknown.

Military public health authorities also monitored disease surveillance trends and febrile illness in deployed service members (Table 2). Final diagnoses were based on clinical assessment, because laboratory capabilities were limited to rapid diagnostic tests for malaria (BinaxNOW, Alere Inc.) and limited blood chemistry and hematology laboratory tests. Testing for Ebola virus by reverse transcription–polymerase chain reaction (RT-PCR) was available for patients with consistent signs and symptoms and an epidemiologic risk factor. Decisions about Ebola testing were made in consultation with U.S. military infectious disease and public health authorities deployed to Liberia.

Approximately 12 hours before departing Liberia, and after verification of compliance with unit monitoring during the preceding 21 days, medical providers screened departing service members for Ebola exposures, fever, and symptoms of possible Ebola, using a separate exit screening form (available at http://www.dtic.mil/whs/directives/forms/eforms/dd2991.pdf) (2). Upon returning to the United States, service members underwent controlled monitoring for 21 days at segregated locations on predesignated U.S. military installations.

DoD Disease Monitoring and Screening Findings

The prevalence of illness among the deployed force averaged 1.8%, with gastrointestinal (33%), respiratory (22%), and dermatologic (20%) conditions accounting for the highest proportions of diagnoses. Thirty-two service members with febrile illness were identified (Table 2), representing 1% of all clinic visits and an estimated febrile illness rate of one case per 9,100 person-days in Liberia (estimated exposure time in Liberia for 2,540 service members was approximately 290,000 person-days, with mean duration of deployment of 110 days). The median time from date of country arrival to fever onset was 30 days (interquartile range = 14–50 days). Twenty (63%) persons reported being within 3 feet of a non-U.S. military person; none reported being within 3 feet of a known ill person or having direct contact with an ill person's skin, blood, or body fluids. Fourteen (44%) febrile patients had never left their access-controlled facility since arriving in Liberia, and five (16%) persons with fever were detected through unit monitoring and unaware that they had fever. None of the 17 (53%) patients with fever and three or more Ebola-compatible symptoms had a close contact with an ill person. After receiving medical care and resolution of fever and symptoms, all patients resumed twice-daily unit monitoring. No febrile patient had an epidemiologic risk factor for Ebola that warranted Ebola RT-PCR testing, although two patients were tested for other reasons (a specimen collection exercise and a medical evacuation requirement) (Table 2). All 32 patients with fever completed a minimum of 21 days of post-fever monitoring by medical personnel.

No deployed service member had contact with a known or suspected Ebola patient, and exit screening on 2,540 persons identified no Ebola exposures, fever, or Ebola symptoms at the time of departure. After completion of an additional 21 days of twice-daily monitoring at controlled monitoring areas in the United States, no Ebola infections were identified.

Discussion

Having been in a country with widespread transmission, deployed service members would be categorized, by CDC criteria, as low (but not zero) risk upon return to the United States. However, based on their non-Ebola care mission and stringent activity restrictions while deployed, they might be at lower risk for exposure than returning U.S. travelers who spent time in Liberia without such restrictions. A comparable assessment of an employer-directed program that actively monitored persons while they worked in an Ebola-affected country has not been published. A report of U.S. airport entry screenings of 1,993 travelers from Ebola-affected countries found that 86 (4%) were referred to CDC public health officers for medical evaluation, seven developed Ebola-compatible symptoms, and none had Ebola (7). This report supports observations that without close contact with an Ebola-infected patient, travel to an Ebola-affected country alone does not place a person at higher risk for Ebola infection.

An advantage of twice-daily monitoring in this deployed setting was that exposure assessments were less likely to be subject to recall bias. In addition, enforced military orders compelling adherence to activity restrictions ensured compliance with the monitoring program. Civilian employers might not have the same capacity to validate temperature, activity, exposure, and symptom history over an extended period of service in an Ebola-affected country. A further benefit of twice-daily symptom and temperature monitoring is that in the event of an Ebola exposure, an infection would be detected early, permitting expedited isolation and more timely treatment and medical evacuation.

Although the precautions put into place to prevent Ebola exposures appear effective, a full assessment of the effectiveness of the monitoring program for Ebola disease is not possible. The accuracy of the screening questionnaire might have been impacted by a respondent's knowledge of a close contact's clinical status. In addition, the potential for secondary gain from not telling the truth, such as avoiding isolation or quarantine, may underestimate exposure risk.

Health ministries in Ebola-affected countries, working directly with CDC and the World Health Organization, have established country exit screening and control measures, which include denying aircraft boarding to ill travelers and persons who report a high Ebola exposure risk (7). Knowledge of the activity restrictions and comprehensive monitoring of deployed U.S. military personnel might better inform clinical decision-making for returning military personnel and increase general awareness for communities receiving them.

1U.S. Joint Forces Command, Operation United Assistance, Monrovia, Liberia; 2Brooke Army Medical Center, Joint Base San Antonio, Fort Sam Houston, Texas.

Corresponding author: Todd J. Vento, todd.j.vento.mil@mail.mil, 210-916-5554.

References

1. CDC. 2014 Ebola outbreak in West Africa—case counts. Available at http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/case-counts.html.
2. US Department of Defense. Memorandum for Under Secretary of Defense. Pre-deployment, deployment, and post-deployment training, screening, and monitoring guidance for Department of Defense personnel deployed to Ebola outbreak areas. Available at http://health.mil/Policies/2014/10/31/Ebola-Screening.
3. CDC. Interim U.S. guidance for monitoring and movement of persons with potential Ebola virus exposure (August 22, 2014). Available at http://www.cdc.gov/vhf/ebola/exposure/monitoring-and-movement-of-persons-with-exposure.html.
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7. Brown CM, Aranas AE, Benenson GA, et al. Airport exit and entry screening for Ebola—August–November 10, 2014. MMWR Morb Mortal Wkly Rep 2014;63:1163–7.