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Retrospective Contact Tracing: A Primer For State And Territorial Health Authorities

Retrospective Contact Tracing: A Primer For State And Territorial Health Authorities

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This policy memo details key features of retrospective contact tracing and lays out five recommendations for state and local public health authorities who are seeking to deploy retrospective tracing as part of their broader contact tracing efforts.

Many states are missing clusters of COVID-19 cases. People are getting sick and dying, and yet, too often policymakers and public health leaders are in the dark about how the virus spreads through their communities. States need better tools to break chains of transmission more quickly and they need better information to make more responsive policy. Contact tracing is a key piece of this puzzle.

Currently, most states are relying solely on prospective or “forward” contact tracing to identify infected individuals. As new cases are detected, professional contact tracers attempt to identify, monitor, and support other individuals who were exposed and may have been infected. However, states have an additional tool at their disposal to break chains of transmission: retrospective or “backwards” contact tracing. Retrospective contact tracing attempts to identify when and where a case was originally infected in an effort to pinpoint COVID-19 clusters, also known as superspreader events. 

Dually deploying both prospective and retrospective contact tracing can save more lives by 1) uncovering how and where clusters are formed, which uncovers more chains of transmission and 2) yielding actionable health intelligence about COVID’s transmission in communities. This health intelligence can better inform precise and impactful responses and public health outcomes statewide, as demonstrated in Massachusetts.

Led by Dr. Margaret Bourdeaux, Research Director of the Program in Global Public Policy and Social Change at Harvard Medical School, BKC Policy Practice: Digital Pandemic Response staff members Alexis Montouris Ciambotti, Adam Nagy, and Hilary Ross worked with student researchers Liza Tarbell and Joyce Wang to produce this policy memo.

The BKC Policy Practice: Digital Pandemic Response program is generously supported by the Ford Foundation, Hewlett Foundation, and the MacArthur Foundation.

For further information and to discuss the content of this memo: contact the Program in Global Public Policy at Department of Global Medicine & Social Change at Harvard Medical School (  

Event Resources

Retrospective Contact Tracing: How States Can Investigate Covid-19 Clusters

On November 12, the Berkman Klein Center for Internet and Society’s Digital Pandemic Response Policy Practice at Harvard University, along with Harvard Medical School’s Program in Global Public Policy and Social Change, the National Governors Association, and Partners In Health’s U.S. Public Health Accompaniment Unit, co-hosted a live event featuring practitioners experienced in implementing prospective and retrospective contact tracing. The policy memo summarizes the lessons learned from this session.

Watch the recording, listen to the audio, or read the transcript here.

Download the Memo

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