(CNN) Thousands of Americans could soon join the ranks of disease detectives in one of the most important battles against coronavirus.

Contact tracing has helped slow or stop previous epidemics, such as the SARS and Ebola outbreaks. But it's never been more critical -- or more challenging -- than in this fight against coronavirus.

Here's how contact tracing works and how it can employ Americans who were recently laid off:

What exactly is contact tracing?

Contact tracing tracks down anyone who might have been infected by a person who was recently diagnosed so those contacts can quarantine themselves and prevent further spread.

"In contact tracing, public health staff work with a patient to help them recall everyone with whom they have had close contact during the timeframe while they may have been infectious," the Centers for Disease Control and Prevention said.

"Contacts are provided with education, information, and support to understand their risk, what they should do to separate themselves from others who are not exposed, monitor themselves for illness, and the possibility that they could spread the infection to others even if they themselves do not feel ill."

It's an arduous task, but contact tracing has been credited with helping stop the SARS epidemic in 2004

But immediate action is needed, the CDC said. "Communities must scale up and train a large contact tracer workforce and work collaboratively across public and private agencies to stop the transmission of COVID-19," the disease caused by novel coronavirus.

Why is contact tracing so critical right now?

Researchers say the US -- or really any country -- can't safely reopen without significant amounts of contact tracing and testing.

Without them, "We're going to be at risk of resurgence of this disease -- not just in the fall, but going into next year," said Josh Michaud, associate director of global health policy at the Kaiser Family Foundation.

How does the process work?

Coronavirus survivor Amy Driscoll got a call from her county health department two hours after she got home from the hospital.

A long list of questions followed: "Who have I seen in the last two weeks? Where was I in the last two weeks? Who was I in contact with? Where do I work?" Driscoll recalled.

After that, her coworkers in Ohio had to be contacted. So did a restaurant where she had gone for lunch. And a hair salon that she had visited. And also those who sat near her at a Cleveland Cavaliers game.

But when contacts are notified, they aren't told who was diagnosed with coronavirus.

"To protect patient privacy, contacts are only informed that they may have been exposed to a patient with the infection," the CDC says. "They are not told the identity of the patient who may have exposed them."

How do people get notified?

Contact tracers use a variety of methods, including phone calls, emails and social media messaging.

Some places are getting creative. In North Dakota, health officials partnered with the creator of an app used to track bison to launch a new app called Care19.

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Those who download Care19 will get a random ID number, "and the app will anonymously cache the individual's locations throughout the day," the North Dakota coronavirus response website says.

"If an individual tests positive for COVID-19, they will be given the opportunity to consent to provide their information to the NDDoH to help in contact tracing and forecasting the pandemic's progression with accurate, real-time data."

Apple and Google are developing new contact tracing technology using smartphones and Bluetooth technology to alert those who may have been close to someone infected.

But there are limitations to that new technology. Users would have to opt-in , and it's not clear whether enough people will do so to make the effort worthwhile. And people without smartphones would not get notified.

How many contact tracers are there?

"The total number of existing disease detectives in the United States (was) only 2,200" before the coronavirus outbreak, said David Harvey, executive director of the National Coalition of STD Directors

About 1,600 of those disease detectives are members of the coalition, which is funded by the CDC and typically combats the spread of sexually transmitted diseases.

But most of them have been redeployed to do contact tracing for coronavirus, Harvey said.

"Any time there's an infectious disease outbreak, they get redeployed to Zika, Ebola, food-borne illness outbreaks," Harvey said. "This is an essential public health workforce."

Do we have enough contact tracers?

No. A study released by Johns Hopkins University estimates the US needs at least 100,000 additional public health workers to help with contact tracing.

And that might be a low estimate, said Anita Cicero, deputy director at the Johns Hopkins Center for Health Security and a co-author of the study. She said the US will likely need more than 100,000, but that's a good start to help the more heavily impacted areas.

Former CDC Director Dr. Tom Frieden said the US could need "several hundred thousand" contact tracers.

The problem: "Both state public health and county local public health do not have the resources or the people that are needed to be able to do contact tracing for all identified cases," Cicero said.

How do I apply to become a contact tracer?

Applicants can go to Contrace.org to submit their information.

"CONTRACE Public Health Corps is a national database of over 50,000 qualified contact tracer applicants," founder and CEO Steve Waters said.

"The information is shared with organizations hiring contact tracing teams throughout the US."

Harvey said you can also check your state health department's website and the CDC Foundation's website for contact tracing job opportunities.

What education do you need to be a contact tracer?

"It is helpful to have a public health or health care background," Harvey said. Fluency in multiple languages is also a plus.

But "no matter what your background, you can be trained to do this work," Harvey said.

Different state or local health departments might have different requirements. The CDC Foundation's job posting requires a bachelor's degree for contact tracing candidates.

How much do contact tracers get paid?

"Contact tracers are not paid enough," Harvey said. "The average salary in the United States is $35,000 a year."

But it is not yet clear how much newly hired contact tracers will make in different parts of the country.

What do contact tracers say to those who might have been exposed?

Sensitivity is important, since it's not easy for people to hear they might have been infected with coronavirus, Harvey said.

"A person will typically be told, 'You may have been exposed. We recommend that you isolate for the next 14 days. Here's where you can get a test. What questions can I answer for you? Tell me folks that you've had sustained closed proximity with, and together we'll work to notify these people,'" he said.

Who's leading contact tracing across the US?

There's no central agency overseeing all the contact tracing -- rather, it's a mix of state and local health departments, nonprofits, private entities and universities.

One of the biggest programs involves New York state, New Jersey, Connecticut, Johns Hopkins Bloomberg School of Public Health, the Resolve to Save Lives Initiative and Bloomberg Philanthropies, which has committed $10.5 million to a new contact tracing program

In Massachusetts, the Boston-based nonprofit Partners in Health is partnering with the state health department to boost contact tracing.

And in San Francisco, the public health department has partnered with the University of California, San Francisco and DIMAGI, a company working with the CDC to digitize workflow and monitoring

Why is contact tracing for coronavirus so difficult?

This coronavirus can also be spread by asymptomatic people who don't look or feel sick , meaning there are carriers who might not even know they're infected.

And unlike contact tracing for other types of diseases, Covid-19 is a respiratory illness. So contact tracers can't knock on people's doors the same way they might have done with other outbreaks, Harvey said.

Does contact tracing actually help?

"Without a doubt, contact tracing works," Harvey said.

Some of the most successful countries in the fight against coronavirus have used widespread contact tracing. By quickly identifying contacts, those who might be infected were able to quarantine themselves and avoid spreading the virus to others.

"This is a strategy that goes hand-in-hand with economic recovery and reducing the isolation recommendations that are currently in place," Harvey said.

"Once people start coming out of their homes and returning to work and resuming aspects of a normal life, that's where this function is essential to measure outbreaks and warn people so we can intervene."