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

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 SARS-CoV-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.