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

  1. Nguyen Van Vinh Chau
  2. Vo Thanh Lam
  3. Nguyen Thanh Dung
  4. Lam Minh Yen
  5. Ngo Ngoc Quang Minh
  6. Le Manh Hung
  7. Nghiem My Ngoc
  8. Nguyen Tri Dung
  9. Dinh Nguyen Huy Man
  10. Lam Anh Nguyet
  11. Le Thanh Hoang Nhat
  12. Le Nguyen Truc Nhu
  13. Nguyen Thi Han Ny
  14. Nguyen Thi Thu Hong
  15. Evelyne Kestelyn
  16. Nguyen Thi Phuong Dung
  17. Tran Chanh Xuan
  18. Tran Tinh Hien
  19. Nguyen Thanh Phong
  20. Tran Nguyen Hoang Tu
  21. Ronald B. Geskus
  22. Tran Tan Thanh
  23. Nguyen Thanh Truong
  24. Nguyen Tan Binh
  25. Tang Chi Thuong
  26. Guy Thwaites
  27. Le Van Tan
  28. for OUCRU COVID-19 research group
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Abstract

Background

Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its contribution to infection transmission.

Methods

We conducted a prospective study at a quarantine centre for COVID-19 in Ho Chi Minh City, Vietnam. We enrolled quarantined people with RT-PCR-confirmed SARS-CoV-2 infection, collecting clinical data, travel and contact history, and saliva at enrolment and daily nasopharyngeal throat swabs (NTS) for RT-PCR testing. We compared the natural history and transmission potential of asymptomatic and symptomatic individuals.

Results

Between March 10 th and April 4 th , 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. 17(57%) participants acquired their infection outside Vietnam. Compared with symptomatic individuals, asymptomatic people were less likely to have detectable SARS-CoV-2 in NTS samples collected at enrolment (8/13 (62%) vs. 17/17 (100%) P=0.02). SARS-CoV-2 RNA was detected in 20/27 (74%) available saliva; 7/11 (64%) in the asymptomatic and 13/16 (81%) in the symptomatic group (P=0.56). Analysis of the probability of RT-PCR positivity showed asymptomatic participants had faster viral clearance than symptomatic participants (P<0.001 for difference over first 19 days). This difference was most pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared to transmit the infection to up to four contacts.

Conclusions

Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit the virus to others.

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