Number Needed to Quarantine and Proportion of Prevented Infectious Days by Quarantine: Evaluating the Effectiveness of COVID-19 Contact Tracing.

Objectives: Information on the effectiveness of COVID-19 contact tracing is lacking. We proposed 2 measures for evaluating the effectiveness of contact tracing and applied them in a public health unit in northern Portugal.

Methods: This retrospective cohort study included the contacts of people with COVID-19 diagnosed July 1-September 15, 2020.