DescriptionSchematic of prospective contact tracing versus prospective and retrospective contact tracing.png
English: An illustration comparing prospective tracing only (A) against combined prospective and
retrospective tracing (B). In both instances, Index Case #1 and Index Case #2 were infected at an (initially) undetected cluster event and detected through standard disease surveillance. The illustration demonstrates how the addition of retrospective tracing can break more transmission chains. In both instances some cases remain undetected due to limitations of contact tracing. This illustration was created by Adam Nagy and is originally available here. This image is a modification of a schematic originally found in Endo et al. “Implication of backward contact tracing in the presence of overdispersed transmission in COVID-19 outbreak.” Wellcome Open Research, (2020), doi: 10.12688/ wellcomeopenres.16344.1
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Possible results of contact tracing are shown comparing (A) only prospective tracing versus (B) both prospective and retrospective tracing are performed.