The natural history and transmission potential of asymptomatic SARS-CoV-2 infection

Abstract

248 2 1 Main text: 2788 2 2 Running title: Asymptomatic SARS-CoV-2 infection 2 3 ABSTRACT 2 5 Background 2 6Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its 2 7 contribution to infection transmission. 2 8 Methods 2 9We conducted a prospective study at a quarantine centre for COVID-19 in Ho Chi Minh City, 3 0 Vietnam. We enrolled quarantined people with RT-PCR-confirmed SARS-CoV-2 infection, 3 1 collecting clinical data, travel and contact history, and saliva at enrolment and daily 3 2 nasopharyngeal throat swabs (NTS) for RT-PCR testing. We compared the natural history and 3 3 transmission potential of asymptomatic and symptomatic individuals.3 4 Results 3 5Between March 10 th and April 4 th , 2020, 14,000 quarantined people were tested for SARS-3 6CoV-2; 49 were positive. Of these, 30 participated in the study: 13(43%) never had symptoms 3 7 and 17(57%) were symptomatic. 17(57%) participants acquired their infection outside Vietnam. 3 8 Compared with symptomatic individuals, asymptomatic people were less likely to have 3 9 detectable SARS-CoV-2 in NTS samples collected at enrolment (8/13 (62%) vs. 17/17 (100%) 4 0 P=0.02). SARS-CoV-2 RNA was detected in 20/27 (74%) available saliva; 7/11 (64%) in the 4 1 asymptomatic and 13/16 (81%) in the symptomatic group (P=0.56). Analysis of the probability 4 2 of RT-PCR positivity showed asymptomatic participants had faster viral clearance than 4 3 symptomatic participants (P<0.001 for difference over first 19 days). This difference was most 4 4 pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared 4 5 to transmit the infection to up to four contacts. 4 6 Conclusions 4 7 Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or 4 8 NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit 4 9 the virus to others. 5 0 Hospitals, located approximately 60 km to the West and East, respectively, of HCMC (Figure 9 7 2A).

Bidirectional contact tracing dramatically improves COVID-19 control

“…Notably, our "optimistic" scenario is more pessimistic than many earlier studies of contact tracing because we assume higher values for both the rate and relative infectiousness of asymptomatic carriers based on numerous recent studies (5,10,27,(31)(32)(33).…”

Evaluating aerosol and splatter following dental procedures: addressing new challenges for oral healthcare and rehabilitation

“…Saliva has been shown to contain severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in infected individuals 22,23 , many of whom may be asymptomatic 24 , with the salivary gland potentially being an early reservoir of infection 25,26 . Equally, however, preliminary data suggest that in asymptomatic carriers, the viral load may be low in saliva and these individuals may have faster viral clearance 27,28 . Early data suggest that SARS-CoV-2 can remain viable and infectious in aerosol for hours, and on surfaces for days 29 .…”

The contribution of asymptomatic SARS-CoV-2 infections to transmission - a model-based analysis of the Diamond Princess outbreak

“…(14) In addition, it is possible that PCR-based testing has a lower sensitivity for asymptomatic infections, which would further increase the proportion of asymptomatic infections. (32) A sensitivity analysis showed that our results were robust to age-specific probabilities of progressing to asymptomatic infections, as well as other assumptions made by the model, and driven by trends in the data.…”

“…(30) cruise While SARS-CoV-2 has been shown to survive on surfaces, (31) but this does not seem to be the primary mode of transmission. In combination with growing evidence around viral load in asymptomatic infections and their involvement in transmission chains (14), anecdotal evidence about transmission from asymptomatic individuals (19,32) including in closed populations, (33) it is reasonable to assume that asymptomatic infections play some role in ongoing SARS-CoV transmission. In our model, 83% of scenarios compatible with the data, asymptomatic infections were responsible for more than half of all transmission.…”