To effectively control the spread of SARS-CoV-2, the virus that causes COVID-19, public health measures such as wearing face masks, social distancing, and handwashing must be combined with repeated and widespread testing. That is the conclusion of a new study in The New England Journal of Medicine by researchers from the Icahn School of Medicine at Mount Sinai and the Naval Medical Research Center, who looked at disease transmission among 1848 Marine recruits between May and July 2020.
The researchers studied the Marine recruits, the majority of whom were male and between the ages of 18 and 20, while they were in a two-week supervised quarantine. The study results, published on November 11, showed that few infected recruits had symptoms before diagnosis of SARS-CoV-2 infection, that transmission occurred despite implementing many best-practice public health measures, and that diagnoses were made only by scheduled tests, not by tests performed in response to the daily temperature checks and symptom screening of the recruits.
“If you rely only on testing you are going to miss cases and the virus will escape, and if you just use public health measures it’s not going to be sufficient,” says the study’s senior author, Stuart Sealfon, MD, the Sara B. and Seth M. Glickenhaus Professor of Neurology at the Icahn School of Medicine at Mount Sinai. “If you do both of them together you should be able to control this highly infectious virus. We hope this information helps in developing more effective measures to keep military installations and schools safe.”
The study data revealed asymptomatic spread of the virus even under strict military orders for quarantine and public health measures that most likely experienced better compliance than would be possible in other youth settings like college campuses. The researchers noted that the virus was largely transmitted within a given platoon group which trained and ate together while maintaining social distancing, handwashing, and other methods of infection control.
The study enrolled participants from nine different Marine recruit classes, each containing 350 to 450 recruits, between May 15 and the end of July. The participants were offered enrollment in a prospective, longitudinal study after self-quarantining at home for two weeks prior to arrival at basic training. Once they arrived, they were required to follow strict group quarantine measures with two-person rooms for two weeks—the duration of the study period—before the start of the actual training. The supervised group quarantine took place at a college used only for this purpose. Each recruit class was housed in different buildings and had different dining times and training schedules, so the classes did not interact.
Each weekly class was further divided into platoons of 50-60. During the study period, all recruits wore cloth masks, practiced social distancing of at least six feet, and regularly washed their hands. Most of their instruction, including exercising and learning military customs and traditions, was done outdoors. After each class finished quarantine, a deep cleaning, using bleach on surfaces, occurred in all rooms and common areas of the dormitories before the arrival of the next class.
To determine asymptomatic and symptomatic SARS-CoV-2 prevalence and transmission during supervised quarantine, participants were tested within 2 days of arrival, at 7 days, and at 14 days using a nasal swab (PCR) test authorized for emergency use by the U.S. Food and Drug Administration. Analysis of viral genomes from infected recruits identified multiple clusters that were temporally, spatially, and epidemiologically linked, revealing multiple local transmission events during quarantine.
“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,” says the study’s co-senior author, 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 spill-over to the wider community, we need to establish widespread initial and repeated surveillance testing of all individuals regardless of symptoms.”
Insight into COVID-19 characteristics and SARS-CoV-2 transmission in military personnel has relevance to developing safer approaches for related settings composed primarily of young adults such as schools, sports, and camps.
This work was supported by the Defense Health Agency through the Naval Medical Research Center and the Defense Advanced Research Projects Agency.