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Original research
Upper respiratory viral load in asymptomatic individuals and mildly symptomatic patients with SARS-CoV-2 infection
  1. Sang Hyun Ra1,
  2. Joon Seo Lim2,
  3. Gwang-un Kim3,
  4. Min Jae Kim1,
  5. Jiwon Jung1,
  6. Sung-Han Kim1
  1. 1Department of Infectious Diseases, Asan Medical Center, University of Ulsan College of Medicine, Songpa-gu, Seoul, Republic of Korea
  2. 2Clinical Research Center, Asan Institute for Life Sciences, Asan Medical Center, Songpa-gu, Seoul, Republic of Korea
  3. 3Health Screening & Promotion Center, Asan Medical Center, Songpa-gu, Seoul, Republic of Korea
  1. Correspondence to Professor Sung-Han Kim, Department of Infectious Diseases, Asan Medical Center, Songpa-gu, Seoul, Korea (the Republic of); kimsunghanmd{at}


Background Asymptomatic individuals with SARS-CoV-2 infection have viable viral loads and have been linked to several transmission cases. However, data on the viral loads in such individuals are lacking. We assessed the viral loads in asymptomatic individuals with SARS-CoV-2 infection in comparison with those in symptomatic patients with COVID-19.

Methods Study participants were recruited from a community facility designated for the isolation of patients with mild COVID-19 in South Korea. The presence of symptoms was evaluated with a questionnaire-based survey. Viral loads in the upper respiratory tract were measured with real-time reverse transcription-PCR (RT-PCR) targeting the E, RdRp and N genes of SARS-CoV-2, with a cycle threshold (Ct) value of 40 for determining positivity.

Results In 213 patients with SARS-CoV-2 infection, 41 (19%) had remained asymptomatic from potential exposure to laboratory confirmation and admission; of them, 39 (95%) underwent follow-up RT-PCR testing after a median 13 days. In 172 symptomatic patients, 144 (84%) underwent follow-up RT-PCR testing. Twenty-one (54%) asymptomatic individuals and 92 (64%) symptomatic patients tested positive for SARS-CoV-2 at follow-up. Asymptomatic individuals and symptomatic patients did not show any significant differences in the mean Ct values of the E (31.15 vs 31.43; p>0.99), RdRp (32.26 vs 32.93; p=0.92) and N (33.05 vs 33.28; p>0.99) genes.

Conclusion Approximately one-fifth of the individuals without severe symptoms were asymptomatic, and their viral loads were comparable to those in symptomatic patients. A large proportion of mildly symptomatic patients with COVID-19 or asymptomatic individuals with SARS-CoV-2 showed persistent positive upper respiratory RT-PCR results at follow-up.

  • viral infection

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  • SHR and JSL contributed equally.

  • Contributors Adminstrative, technical or logistic support: SHR, JSL, MJK, JJ; analysis and interpretation of the data: SHR, JSL, S-HK; collection and assembly of data: SHR, JSL, MJK, JJ; concept and design: S-HK; clinical revision for important intellectual content: SHR, JSL, MJK, JJ, S-HK.

  • Funding This study was supported by a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number HW20C2062).

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval IRB of Asan Medical Center (2020-0336).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request. Deidentified participant data.

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