Recent Studies Look at Marine Recruits, Aircraft Carrier Outbreak
Masked sailors man the rails as the aircraft carrier USS Theodore Roosevelt arrives at Naval Air Station North Island this summer. A COVID-10 on the ship prompted the Navy to change is infection control procedures. Navy photo by Mass Communication Specialist Seaman Olympia O. McCoy
SILVER SPRING, MD — What happened with 2,000 Marine recruits who went through supervised quarantine before starting basic training is providing critical insights into the effectiveness of public health measures to suppress transmission of COVID-19 among young adults, whether in military training, schools or other groups.
Several instances of asymptomatic transmission of SARS-CoV-2, the virus that causes COVID-19, occurred among those recruits despite the quarantine measures.
An article in The New England Journal of Medicine reported that few of the infected recruits had symptoms before diagnosis of SARS-CoV-2 infection and that diagnoses usually were made only by scheduled tests, not in response to symptoms. The Naval Medical Research Center-led studies also emphasized that virus transmission occurred despite implementing many best-practice public health measures.1
“This is a difficult infection to suppress in young people, even with close supervision of their mask wearing, social distancing and other mitigation measures,” explained co-author Stuart Sealfon, MD, of the Icahn School of Medicine at Mount Sinai in New York. “We find that regular testing not dependent on symptoms identifies carriers who can transmit SARS-CoV-2. We hope this information helps in developing more effective measures to keep military installations and schools safe.”
The authors pointed out that the effectiveness of public health measures to control the transmission of SARS-CoV-2 has not been well studied in young adults, which prompted their research. The investigation involved SARS-CoV-2 infections among U.S. Marine Corps recruits who underwent a two-week quarantine at home, followed by a second supervised two-week quarantine at a closed college campus that involved mask wearing, social distancing and daily temperature and symptom monitoring.
Testing for SARS-CoV-2 was by quantitative polymerase-chain-reaction (qPCR) assays of nares swab specimens; tests occurred between the time of arrival and the second day of supervised quarantine and on Days 7 and 14 in 1,848 recruits who volunteered for the study. Those who did not underwent qPCR testing only on Day 14, at the end of the quarantine period.
Researchers also performed phylogenetic analysis of viral genomes obtained from infected study volunteers to identify clusters and to assess the epidemiologic features of infections.
Of those volunteering to participate in the study; within two days after arrival on campus, 16 (0.9%) tested positive for SARS-CoV-2, 15 of whom were asymptomatic. The authors noted that another 35 participants (1.9%) tested positive on Day 7 or on Day 14. Yet only 5 of the 51 participants (9.8%) who tested positive at any time had symptoms in the week before a positive qPCR test, they reported.
Among recruits who declined to participate in the study, 26 (1.7%) of the 1,554 recruits with available qPCR results tested positive on Day 14, although no SARS-CoV-2 infections were identified through clinical qPCR testing performed as a result of daily symptom monitoring.
The study also discussed analysis of 36 SARS-CoV-2 genomes obtained from 32 participants, which revealed six transmission clusters among 18 participants. Researchers said that epidemiologic analysis suggested multiple local transmission events, including transmission between roommates and among recruits within the same platoon.
“Among Marine Corps recruits, approximately 2% who had previously had negative results for SARS-CoV-2 at the beginning of supervised quarantine, and less than 2% of recruits with unknown previous status, tested positive by day 14,” the authors concluded. “Most recruits who tested positive were asymptomatic, and no infections were detected through daily symptom monitoring. Transmission clusters occurred within platoons.”
Participants who were associated with the two largest transmission clusters (clusters 2 and 5) were identified by means of sequencing and were either roommates or members of the same platoons, which indicates that double-occupancy rooming and shared platoon membership were important contributors to transmission. Other infected members of these platoons whose samples were not sequenced may have been infected with the same cluster strains. One recruit in each platoon was found to be infected at the beginning of quarantine and represents the potential source of each cluster strain.
Confined Living Spaces
They added, “U.S. Department of Defense installations have implemented recommended public health interventions. However, confined living spaces, close contact among persons during training regimens and other activities, shared dining facilities, and mixing of persons from across the United States place military populations at risk for contracting contagious respiratory infections such as coronavirus disease 2019 (COVID-19).”
“The identification of six independent transmission clusters defined by distinct mutations indicates that there were multiple independent SARS-CoV-2 introductions and outbreaks during the supervised quarantine,” explained Harm van Bakel, PhD, assistant professor of genetics and genomic sciences at the Icahn School of Medicine at Mount Sinai. “The data from this large study indicates that, in order to curtail coronavirus transmission in group settings and prevent spillover to the wider community, we need to establish widespread initial and repeated surveillance testing of all individuals regardless of symptoms.”
The authors pointed out that the information gathered about COVID-19 characteristics and SARS-CoV-2 transmission in military personnel will be helpful in developing safer approaches for other settings made up of young adults such as schools, sports and camps.
During the quarantine of nine Marine Corps recruit classes—involving a population of 3,402 recruits—recruits were under the constant supervision of Marine Corps instructors. Researchers noted that level of supervision was unlikely to occur in other settings in which young adults congregate, however.
Another New England Journal of Medicine article discussed the outbreak of coronavirus disease 2019 (COVID-19) occurred on the U.S.S. Theodore Roosevelt, a nuclear-powered aircraft carrier with a crew of 4,779 personnel.2
For the study, researchers gathered clinical and demographic data for all crew members, including results of testing by real-time reverse-transcriptase polymerase chain reaction (rRT-PCR). Follow-up occurred for a minimum of 10 weeks, regardless of test results or the absence of symptoms.
Mean age was 27 years, with most of the young crew members in general good health, meeting U.S. Navy standards for sea duty. During the outbreak, 1,271 crew members—26.6%—tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection by rRT-PCR testing, with more than 1,000 infections identified within five weeks after the first laboratory-confirmed infection. An additional 60 crew members had suspected COVID-19, defined as meeting Council of State and Territorial Epidemiologists clinical criteria for COVID-19 without a positive test.
Among those with laboratory-confirmed infection, 76.9% (978 of 1271) had no symptoms at the time they tested positive, and only 55.0% had symptoms develop at any time during the clinical course. A very small percentage, 1.7, were hospitalized, with four requiring intensive care and one dying.
The authors pointed out that crew members who worked in confined spaces appeared more likely to become infected.
“SARS-CoV-2 spread quickly among the crew of the U.S.S. Theodore Roosevelt. Transmission was facilitated by close-quarters conditions and by asymptomatic and presymptomatic infected crew members. Nearly half of those who tested positive for the virus never had symptoms,” researchers concluded.
Noting that the epidemiology of SARS-CoV-2 infection in young, healthy populations has not been studied extensively, the study suggested that the outbreak of COVID-19 on the U.S.S. Theodore Roosevelt provided an unusual opportunity to assess an outbreak in a predominantly young, healthy, working-age population.
The great majority, 69%, of crew members were younger than 30 years of age, and no crew member was older than 65 years, according to the report, and all were up to date with their immunizations.
“Not surprisingly, crew members working in the engine room and other confined areas of the ship faced a higher risk of being infected than their shipmates on deck,” according to the researchers. “A study conducted by the Navy and Marine Corps Public Health Center and the CDC, involving 384 volunteer U.S.S. Theodore Roosevelt crew members, showed similar results: those working in confined spaces had higher odds of contracting COVID-19.”
The lack of symptoms among most infected crew members and the lack of recognition by sailors with unusual or atypical symptoms made it difficult to control the outbreak, according to the report.
“These observations suggest that non-symptomatic or mildly symptomatic crew members played an important role in the rapid spread of the outbreak, much as young adults with asymptomatic infection appear to contribute to spread in civilian populations,” the authors concluded.
The study also described how the Navy has launched several procedures to create and sustain COVID-19–free environments on its ships. For example, before deployment, all members of a ship’s crew are placed in “restriction of movement,” and most avoid community exposure for 14 days. To identify asymptomatic or presymptomatic carriers, the Navy added rRT-PCR testing at the end of the “restriction of movement” period. Furthermore, Navy ships have sharply reduced shore leaves at foreign ports to prevent crew members from bringing the virus on board.
The result has been the deployment of Since these policies (along with preventive measures of mask use, social distancing multiple ships without sustaining another serious outbreak.
A related commentary discussed how the two articles demonstrate how medical practices used in the military could inform civilian public health practices with respect to shared living situations during the COVID-19 pandemic.3
The author, Nelson L. Michael, MD, PhD, of the Walter Reed Army Institute of Research in Silver Spring, MD, wrote, “The approaches learned from the U.S.S. Theodore Roosevelt and Parris Island can be applied, with varying degrees of relevance, to land-based shared living situations such as college dormitories, prisons, and residential care facilities, as well as sports training environments, meat-processing facilities, and isolated energy plants.”
Additional studies are needed to understand the durability of natural immunity and the durability of immunity from vaccination or passive immunotherapy, when data are available. The addition of these pharmaceutical interventions to the available public health tools will help control the pandemic and safely open societies. Only the scientific analysis of the epidemiology of infection in such shared living environments with these new diagnostic, preventive, and therapeutic interventions will allow for sound policy decisions in the response to the COVID-19 pandemic as well as subsequent pandemics of respiratory viruses to come.
- Letizia AG, Ramos I, Obla A, Goforth C, et. Al. SARS-CoV-2 Transmission among Marine Recruits during Quarantine. N Engl J Med. 2020 Nov 11. doi: 10.1056/NEJMoa2029717. Epub ahead of print. PMID: 33176093.2.
- Kasper MR, Geibe JR, Sears CL, Riegodedios AJ, et. Al. An Outbreak of COVID-19 on an Aircraft Carrier. N Engl J Med. 2020 Nov 11. doi: 10.1056/NEJMoa2019375. Epub ahead of print. PMID: 33176077.
- Michael NL. SARS-CoV-2 in the U.S. Military – Lessons for Civil Society. N Engl J Med. 2020 Nov 11. doi: 10.1056/NEJMe2032179. Epub ahead of print. PMID: 33176076.
