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. 2023 May 22. Online ahead of print. doi: 10.1016/j.jfma.2023.05.018

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© 2023 Formosan Medical Association. Published by Elsevier Taiwan LLC.

Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 3 — The framework of bi-directional contact tracing (a) a contact elicitation window of 2 days is used to ensure more infected contacts are identified, thus day 0 is considered as 2 days prior to the date of symptom onset or specimen collection for SARS-CoV-2 testing for the index case.⁶²^,⁶³ (b) close contacts are defined as individuals with face-to-face contact (within 2 m) for a period of ≥15 min or direct exposure to aerosols or respiratory secretions without proper personal protection equipment from 2 days before the onset date of index case to the start of isolation. (c) The quarantine period of contacts is adjusted from 14 days to balance the public health risks and benefits against the social and economic impact.