Abstract
BackgroundLittle is known about the natural history of asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.MethodsWe conducted a prospective study at a quarantine center for coronavirus disease 2019 in Ho Chi Minh City, Vietnam. We enrolled quarantined people with reverse-transcription polymerase chain reaction (RT-PCR)–confirmed SARS-CoV-2 infection, collecting clinical data, travel and contact history, and saliva at enrollment and daily nasopharyngeal/throat swabs (NTSs) for RT-PCR testing. We compared the natural history and transmission potential of asymptomatic and symptomatic individuals.ResultsBetween 10 March and 4 April 2020, 14 000 quarantined people were tested for SARS-CoV-2; 49 were positive. Of these, 30 participated in the study: 13 (43%) never had symptoms and 17 (57%) were symptomatic. Seventeen (57%) participants imported cases. Compared with symptomatic individuals, asymptomatic people were less likely to have detectable SARS-CoV-2 in NTS collected at enrollment (8/13 [62%] vs 17/17 [100%]; P = .02). SARS-CoV-2 RNA was detected in 20 of 27 (74%) available saliva samples (7 of 11 [64%] in the asymptomatic group and 13 of 16 [81%] in the symptomatic group; P = .56). Analysis of RT-PCR positivity probability showed that asymptomatic participants had faster viral clearance than symptomatic participants (P < .001 for difference over the first 19 days). This difference was most pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared to transmit SARS-CoV-2 to 4 contacts.ConclusionsAsymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or NTSs. The NTS viral loads fall faster in asymptomatic individuals, but these individuals appear able to transmit the virus to others.
Highlights
Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its contribution to infection transmission
Asymptomatic people were less likely to have detectable SARS-CoV-2 in nasopharyngeal throat swabs (NTS) samples collected at enrolment (8/13 (62%) vs. 17/17 (100%)
NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit the virus to others
Summary
Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its contribution to infection transmission. The rapid global spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has prompted the World Health Organization to declare a pandemic. As of April 23rd, 2020, more than 2.6 milllion confirmed cases and more than 180,000 deaths have been reported globally. The clinical syndrome caused by SARS-CoV-2 is called COVID-19 [3], an infectious disease which varies from mild to severe, life-threatening respiratory infection. SARS-CoV-2 infected patients can be infectious prior to symptom (COVID-19) development and cause transmission [8, 9]. There is some evidence demonstrating the transmisson potential of those with RT-PCR confirmed infection who never develop symptoms during their infection (asymptomatic transmission) [4, 5, 7], suggesting asymptomatic infection may play an important role in the spread of SARS-CoV-2
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