The U.S. may need 100,000 people trained in the public health practice of contact tracing — tracking and isolating people who've been in contact with someone who tests positive for the coronavirus. NPR health policy reporter Selena Simmons-Duffin explains how it works, and why it's a key part of the fight against the pandemic. Email the show at [email protected]. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy