A study of nearly 2,000 US Marine Corps recruits who underwent a strict phased quarantine before starting basic training identified several cases of asymptomatic COVID-19 spread, suggesting the need for the development of safer methods for similar settings involving young adults, including schools, sports, and camps, amid the pandemic.
In the study, published yesterday in the New England Journal of Medicine, researchers at the Icahn School of Medicine at Mount Sinai Hospital and the Naval Medical Research Center studied 1,848 study volunteers during a supervised quarantine at a closed South Carolina college campus after they had quarantined at home for 2 weeks. Each participant was tested for SARS-CoV-2, the virus that causes COVID-19, on days 2, 7, and 14.
The college quarantine consisted of wearing face coverings, physical distancing, regular handwashing, and daily temperature and symptom monitoring. Two trainees were housed in each dorm room, and each recruit class was housed in a different building and dined and trained at different times, so there was no interaction among them. All spaces were cleaned between classes, and most exercise and training was done outdoors.
Of the 1,848 participants from nine different Marine recruit classes studied from May 15 to Jul 31, 16 (0.9%) tested positive for COVID-19 within 2 days of arrival on campus, 15 (94%) of whom had no symptoms. Another 35 recruits (1.9%) received positive results on days 7 or 14. Five of all 51 recruits (9.8%) who tested positive during the study reported having coronavirus symptoms in the week before testing positive.
Of the 1,554 recruits who didn't participate in the study but had available test results, 26 (1.7%) tested positive on day 14. No COVID-19 infections were identified through routine testing conducted during daily symptom monitoring.
Value of repeated asymptomatic surveillance testing
Analysis of the 36 coronavirus genomes from 32 participants revealed six transmission events involving 18 recruits, and epidemiologic analysis supported that finding, with spread among roommates and recruits in the same 50- to 60-person platoons.
The authors said the findings show that transmission occurred despite the use of many infection-control best practices, the adherence to which was likely better than would be seen in other young adult settings such as college dorms, and that tests performed in response to coronavirus symptoms identified no infections—unlike regularly scheduled tests.
Coauthor Harm van Bakel, PhD, of the Icahn School, said in an Icahn news release that the identification of COVID-19 infection clusters defined by distinct mutations illustrates the often-silent spread of the virus, which can be disastrous within the close quarters of a ship.
"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," van Bakel said.
Lead author Cmdr. Andrew Letizia, MD, of the Navy Medical Research Center, said in the release that the study results should guide development of more rigorous infection-control measures among young adults in congregate-living settings. "These results 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," he said.
Need for longer predeployment quarantines
In a commentary in the same journal, Col. Nelson Michael, MD, PhD, of the Walter Reed Army Institute of Research, said that the identification of late COVID-19 infections during the supervised quarantine is a sign that the recruits should have been quarantined longer than 2 weeks.
"An extended quarantine may prevent further transmission once recruits enter a prolonged training period on base, where physical distancing is far more difficult to reconcile with the need to train combat infantry," he said.
Michael added that scientific analysis of the epidemiologic factors of congregate living environments and the development of 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."