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. 2021 Mar 31;5:239. Originally published 2020 Oct 13. [Version 3] doi: 10.12688/wellcomeopenres.16344.3

Figure 1. Schematic illustration of forward and backward contact tracing.

Figure 1.

Two cases (index cases #1 and #2) from a transmission tree originating from an (initially) undetected primary case are assumed to be detected by surveillance. Possible results of contact tracing are shown where ( A) only forward tracing is performed or ( B) both forward and backward tracing are performed. Some cases may remain undetected because contact tracing can miss cases.