The Berkman Klein Center’s Digital Pandemic Response<https://cyber.harvard.edu/programs/bkc-policy-practice-digital-pandemic-response> program recently co-hosted an event on “Retrospective Contact Tracing: How States Can Investigate Covid-19 Clusters<https://cyber.harvard.edu/events/retrospective-contact-tracing-how-states-can-investigate-covid-19-clusters>” exploring how U.S. state and local public health leaders can implement retrospective contact tracing to better identify Covid-19 clusters and mitigate their spread. The event featured experts and practitioners Drs. Hitoshi Oshitani, KJ Seung, Margaret Bourdeaux, and Professor Zeynep Tufekci. You can find video and audio recording along with a transcript of the event here<https://cyber.harvard.edu/events/retrospective-contact-tracing-how-states-can-investigate-covid-19-clusters>.

Dr. Bourdeaux and members of our team drafted a short policy memo<https://cyber.harvard.edu/story/2020-11/retrospective-contact-tracing-primer-state-and-territorial-health-authorities> summarizing lessons from the event, detailing key features of retrospective contact tracing, and laying 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. More information is below and here<https://cyber.harvard.edu/story/2020-11/retrospective-contact-tracing-primer-state-and-territorial-health-authorities>.

What Are Prospective and Retrospective Contact Tracing?
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.

How Can Retrospective Contact Tracing Help?
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. Read the memo<https://cyber.harvard.edu/story/2020-11/retrospective-contact-tracing-primer-state-and-territorial-health-authorities> for more information on retrospective tracing and recommendations on implementation.

More Information
Led by Dr. Margaret Bourdeaux, Research Director of the Program in Global Public Policy and Social Change at Harvard Medical School<https://ghsm.hms.harvard.edu/programs/public-policy>, BKC Policy Practice: Digital Pandemic Response<https://cyber.harvard.edu/programs/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<https://cyber.harvard.edu/story/2020-11/retrospective-contact-tracing-primer-state-and-territorial-health-authorities>.

The BKC Policy Practice: Digital Pandemic Response<https://cyber.harvard.edu/programs/bkc-policy-practice-digital-pandemic-response> program is generously supported by the Ford Foundation, Hewlett Foundation, and the MacArthur Foundation.