J Korean Med Sci.  2021 Aug;36(33):e233. 10.3346/jkms.2021.36.e233.

Frequent Occurrence of SARS-CoV-2 Transmission among Non-close Contacts Exposed to COVID-19 Patients

  • 1Department of Infectious Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
  • 2Office for Infection Control, Asan Medical Center, Seoul, Korea
  • 3Department of Microbiology, Institute for Viral Diseases, Biosafety Center, College of Medicine, Korea University, Seoul, Korea
  • 4Department of Laboratory Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission among non-close contacts is not infrequent. We evaluated the proportion and circumstances of individuals to whom SARS-CoV-2 was transmitted without close contact with the index patient in a nosocomial outbreak in a tertiary care hospital in Korea. From March 2020 to March 2021, there were 36 secondary cases from 14 SARS-CoV-2 infected individuals. Of the 36 secondary cases, 26 (72%) had been classified as close contact and the remaining 10 (28%) were classified as non-close contact. Of the 10 non-close contact, 4 had short conversations with both individuals masked, 4 shared a space without any conversation with both masked, and the remaining 2 entered the space after the index had left. At least one quarter of SARSCoV-2 transmissions occurred among non-close contacts. The definition of close contact for SARS-CoV-2 exposure based on the mode of droplet transmission should be revised to reflect the airborne nature of SARS-CoV-2 transmission.


SARS-CoV-2; COVID-19; Contact Tracing; Close Contact
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