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Asymptomatic SARS-CoV-2 Spread Common in Close Quarters, US Military Studies Suggest

NEW YORK – Two studies by independent research teams are revealing new details on the spread of SARS-CoV-2 within military personnel or trainees, including thousands of members of the US Navy who were affected by an aircraft carrier outbreak this spring as well as new Marine recruits under strict quarantine.

In one of the papers, published in the New England Journal of Medicine on Wednesday, a team led by the US Navy Bureau of Medicine and Surgery and the Navy and Marine Corps Public Health Center outlined the extent of the SARS-CoV-2 outbreak on the USS Theodore Roosevelt aircraft carrier from late March to mid-May.

"Our findings offer insights into the epidemiology and outcomes of SARS-CoV-2 infection in healthy, fit, military-aged adults who are housed in close quarters," first and corresponding author Matthew Kasper, a researcher with the US Navy Bureau of Medicine and Surgery, and his colleagues wrote.

With real-time RT-PCR testing on nasopharyngeal swab samples, the team identified 1,271 SARS-CoV-2-positive crew members over the course of the outbreak, which was first detected when three individuals with COVID-19 symptoms visited the ship's medical department.

Despite quickly quarantining some 400 individuals who had been in contact with the three patients, the researchers explained, SARS-CoV-2 spread to at least 1,000 more crew members over the following five weeks. Another 60 individuals came down with suspected, but not lab-confirmed SARS-CoV-2 infections.

Over half of those infected experienced symptoms at some point, and 1.7 percent required hospitalization, though almost 77 percent were symptom-free at the time of diagnosis. One crew member died, and four more spent time in intensive care.

The authors noted that another 4,079 crew members who tested negative for SARS-CoV-2 at least once were quarantined in single rooms at off-base hotels in Guam or on the Naval Base Guam. Of the 4,779 crew members originally aboard the USS Theodore Roosevelt, 3,448 remained SARS-CoV-2-free over the course of the outbreak.

"Since this outbreak occurred, the US Navy has incorporated lessons learned to enhance the safety and readiness of its crews," the authors noted, adding that ship crews are now "placed in 'restriction of movement' and insulated from community exposure for 14 days" prior to deployment to minimize the risk of spread by symptom-free virus carriers. 

Based on the USS Theodore Roosevelt experience and other notable outbreaks, they also concluded that "[o]rganizations seeking to safeguard their employees, customers, patients, or students may benefit from assuming that COVID-19 will be introduced into their populations and rigorously enforcing measures to minimize viral transmission by all, since persons may be unaware that they are infected."

In a related NEJM paper, investigators at the Naval Research Center, Uniformed Services University, Icahn School of Medicine at Mount Sinai, and elsewhere presented findings from the "COVID-19 Health Action Response for Marines" (CHARM) study. 

That effort stemmed from the realization that "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 authors explained. 

For CHARM, the researchers performed qPCR and antibody testing on nasal swab and blood samples, respectively, that were collected over time to track SARS-CoV-2 transmission in 1,848 Marine recruits, representing nine incoming classes. The recruits took part in two rounds of quarantine — two weeks at home as well as two weeks of supervised quarantine with mask wearing, distancing, temperature checks, and more on campus — and needed a negative SARS-CoV-2 qPCR test before starting basic training at a Marine Corps Recruit Depot on South Carolina's Parris Island.

"The public health program implemented by the US Marine Corps for all new recruits includes a period of home quarantine followed by a [two]-week, strictly supervised quarantine at a closed campus, with the objective of mitigating infection among recruits," the authors explained.

On the first day on campus, after two weeks of home quarantine, the team identified 16 recruits with SARS-CoV-2. All but one of the individuals was symptom-free. Over the following two weeks, another 35 study participants tested positive for SARS-CoV-2 using the qPCR-based assay and nasal swab approach, as did 26 of the 1,554 recruits who opted against participating in the full study. 

Fewer than one in 10 individuals with a positive SARS-CoV-2 test reported COVID-19 symptoms in the week leading up to their positive test, the researchers reported, and daily symptom monitoring during the on-campus quarantine did not uncover any SARS-CoV-2 cases.

"We find that regular testing not dependent on symptoms identifies carriers who can transmit SARS-CoV-2," co-senior and corresponding author Stuart Sealfon, a neurology researcher at the Icahn School of Medicine, said in a statement. "We hope this information helps in developing more effective measures to keep military installations and schools safe."

Using SARS-CoV-2 genome sequence data from 32 SARS-CoV-2-positive individuals, they were able to identify half a dozen main transmission clusters that could explain infections in 18 of the individuals.

"The data from this large study indicates that in order to curtail coronavirus transmission in group settings and prevent spill-over to the wider community, we need to establish widespread initial and repeated surveillance testing of all individuals regardless of symptoms," co-senior author Harm van Bakel, a genetics and genomics researcher at the Icahn School of Medicine, said in a statement.

The study's first author, Commander Andrew Letizia, deputy director of the Naval Medical Research Center infectious disease directorate, added in a statement that the findings "will improve the medical readiness of our Marines and should help inform public health policy across the Navy, Department of Defense, and society at large to decrease transmission of SARS CoV-2."

In a NEJM editorial, Nelson Michael, director of the Walter Reed Army Institute of Research's Center for Infectious Diseases Research, called for military infection control measures that are informed by these and other epidemiological studies in order to safely support those involved in military training and operations during the ongoing COVID-19 pandemic.

But he also emphasized the importance of drawing from such examples when designing safe approaches to non-military situations that involve individuals living or working in close quarters, including prisons, dormitories, care facilities, and sports teams.

"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," Michael concluded.