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SARS-CoV-2 Transmission among Marine Recruits during Quarantine
Andrew G Letizia1, Irene Ramos1, Ajay Obla1
1From the Naval Medical Research Center, Silver Spring (A.G.L., C.G., D.L.W., L.E., W.D.G., R.G., F.J., J.M., E.N., B.L.P., C.P., J.R., E.S.A., M.P.S., V.S., C.W.) and the Infectious Disease Clinical Research Program, Uniformed Services University (E.V.M.), Bethesda - both in Maryland; the Naval Medical Research Unit 6, Lima, Peru (R.L., S.L.); the Departments of Neurology (I.R., Y.G., M.-C.G., A.K., N.M., V.D.N., G.N., S.R., A.S.-S., S.V., S.C.S.) and Genetics and Genomic Sciences (A.O., J.D., E.E., A.S.G.-R., A.G., R.S., H.B.), Icahn Institute for Data Science and Genomic Technology (E.E., R.S., H.B.), the Black Family Stem Cell Institute, Icahn School of Medicine at Mount Sinai (R.S.), and the Center for Computational Biology, Flatiron Institute (R.S.G.S., O.G.T.) - all in New York; the University of Alabama at Birmingham Center for Exercise Medicine, University of Alabama Medical School, Birmingham (M.M.B.); Sema4, Stamford, CT (R.S.); the Navy Medicine Readiness and Training Command Beaufort, Beaufort, SC (M.T.); and the Lewis-Sigler Institute for Integrative Genomics, Princeton, NJ (O.G.T.).
Background:
The efficacy of public health measures to control the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has not been well studied in young adults.
Methods:
We investigated SARS-CoV-2 infections among U.S. Marine Corps recruits who underwent a 2-week quarantine at home followed by a second supervised 2-week quarantine at a closed college campus that involved mask wearing, social distancing, and daily temperature and symptom monitoring. Study volunteers were tested for SARS-CoV-2 by means of quantitative polymerase-chain-reaction (qPCR) assay of nares swab specimens obtained between the time of arrival and the second day of supervised quarantine and on days 7 and 14. Recruits who did not volunteer for the study underwent qPCR testing only on day 14, at the end of the quarantine period. We performed phylogenetic analysis of viral genomes obtained from infected study volunteers to identify clusters and to assess the epidemiologic features of infections.
Results:
A total of 1848 recruits volunteered to participate in the study; within 2 days after arrival on campus, 16 (0.9%) tested positive for SARS-CoV-2, 15 of whom were asymptomatic. An additional 35 participants (1.9%) tested positive on day 7 or on day 14. Five of the 51 participants (9.8%) who tested positive at any time had symptoms in the week before a positive qPCR test. Of the recruits who declined to participate in the study, 26 (1.7%) of the 1554 recruits with available qPCR results tested positive on day 14. No SARS-CoV-2 infections were identified through clinical qPCR testing performed as a result of daily symptom monitoring. Analysis of 36 SARS-CoV-2 genomes obtained from 32 participants revealed six transmission clusters among 18 participants. Epidemiologic analysis supported multiple local transmission events, including transmission between roommates and among recruits within the same platoon.
Conclusions:
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. Most recruits who tested positive were asymptomatic, and no infections were detected through daily symptom monitoring. Transmission clusters occurred within platoons. (Funded by the Defense Health Agency and others.).
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