What is contact tracing?

And how can it slow COVID-19?

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Public health officials are touting social distancing, staying at home and other measures to combat the virus — but experts including former CDC director Dr. Tom Frieden agree that a practice called contact tracing will be key to stopping the spread of the virus in the United States.

"As we move into the suppression phase of our COVID-19 response, there will be a need for testing and contact tracing to protect people from the spread of the virus," Frieden said. "There is a need for speed. The U.S. must scale up its ability to conduct contact tracing immediately in order to protect families and communities."

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Healthcare workers with the University of Nevada Las Vegas School of Medicine wait in personal protective equipment for patients at a drive-thru coronavirus testing site Tuesday, March 24, 2020, in Las Vegas. (AP Photo/John Locher)

Contract tracing is the painstaking process of identifying, contacting and in some cases isolating people who have been near an infected individual. Now that coronavirus has been in the community spread stage for weeks, contact tracing can prove to be quite a job for the local health departments carrying it out.

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“Contact tracing is the bread and butter of public health; it’s also incredibly difficult," Frieden told FOX Business in a statement.

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In West Virginia, which had 191 coronavirus cases as of Wednesday, the National Guard is stepping in to help with contact tracing and other needs.

In this April 1, 2020, photo, a passenger holds up a green pass on their phone on a subway train in Wuhan in central China's Hubei province. (AP Photo/Olivia Zhang)

Meanwhile, China, the origin of the outbreak, is using digital technology as a form of contact tracing. Wuhan has linked residents' coronavirus status to their smartphones to keep them at home if they have been exposed or even diagnosed with the virus.

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