SACRAMENTO, Calif. - As California hurries to reopen stores, offices, restaurants and more, another rush is on behind-the-scenes.

State health officials have launched an unprecedented effort to train thousands of front-line, county-level workers to act as a firewall to stop the coronavirus from roaring back this fall.

Commonly known in the public health world as communicable-disease "contact tracers," this ad hoc group will serve as community strike teams in each county, working on tight deadlines to stop individual infections from turning into major outbreaks.

When someone tests positive for COVID-19, the tracing team will interview that person, find out who they have been in close contact with, then quickly call each of those people to tell them they have been exposed to the virus and to instruct them to take a coronavirus test. If tests come out positive, individuals will be asked to stay home for two weeks, and the whole cycle begins again. Some counties, though, will simply instruct the person to self-quarantine without taking the test.

It means cold-calling people who may be frightened or distrustful of the government. Some will likely hang up when they hear who's on the other line.

Health experts say contact tracers, combined with more robust testing, are the necessary one-two punch that will hold the virus at bay as the economy reopens.

"The more human interaction we're having, the higher risk for transmission," Yolo County public health director Brian Vaughn said. "The ability to test and track those who are in contact (with infected people) is critical for it not to blow up again."

It's a tightrope walk over potentially lethal terrain. Gov. Gavin Newsom and state health officials say they are confident the process can help slow a spread of the virus.

But they also have their fingers crossed.

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For now, the state is building its contact tracing army mainly with existing government employees transferred from other jobs. Some are librarians, sheriff deputies and school nurses temporarily reassigned to the vital task. But others may be new hires at low wages, and some may even be volunteers.

Each tracer is receiving 20 hours of online training. But it is uncertain how many tracers the state needs or how quickly they can be integrated into each county's coronavirus monitoring team.

The governor in recent days has said the state may need to find, hire and train up to 20,000 people, starting with a first major push this week. On May 18, Newsom said the state already had more than 2,800 tracers on hand and another 500 had been trained in recent weeks, ready to be deployed.

A second uncertainty surrounds testing, which has been a weak link since the beginning of the epidemic three months ago. Contact tracing can only be successful if a county has robust testing that catches new infections quickly.

If the state or counties fail to persuade people in rural areas, poorer areas or those who frequent congregate settings - such as nursing homes, churches, or group events - to get tested, individual cases can quickly turn into infection clusters with ripple effects to entire communities.

Contact tracing is not new in the health and epidemiology world. Almost every California county had at least one contact tracer prior to the coronavirus.

Their task has been to quell outbreaks of measles, HIV or AIDS, sexually transmitted diseases and other rarer transmittable diseases, such as tuberculosis, using the same techniques that will be used for the coronavirus tracing. In 2015 and 2016, contact tracers played a key role in stopping the Ebola crisis in Africa.

"Contact tracing is not new to us, we are just at a scale that is unprecedented," said Dr. Melissa Marx, who heads the Surveillance Outbreak Response Team at the Johns Hopkins Bloomberg School of Public Health.

Counties have been creative, searching their existing county staff for people with useful skills and who may have lighter workloads during the pandemic. Shasta County officials drafted criminal investigators from the district attorney's office, school nurses and some sheriff's deputies.

The nurses understand health science, plus they had free time with schools being closed, said Shasta County health department spokeswoman Kerri Schuette. The sheriff's deputies and criminal investigators are good at talking to people.

"It's a blend of an investigative- and people-skills team," Schuette said.

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Prior to the coronavirus pandemic, almost no county in the state had enough contact tracers on its current staff to do the job expected in the coming year.

The state health department announced two weeks ago, to the shock of many county health officials, that each county should have 15 contact tracers per 100,000 residents before it reopens restaurants and stores for interior patronage.

For Sacramento County, which had six tracers, that would mean ramping up to 230 within weeks.

Sacramento County health chief Dr. Peter Beilenson said he thinks that may be overkill and said he doesn't want the state to hold back on reopening the economy based on a number that may not be necessary.

The county has expanded their team to more than 30 contact tracers by retraining existing county employees who have the research and people skills to handle the job. For the moment, Beilenson said, that may be enough. In the last few days, the county has seen only a handful of new cases daily and Sacramento now plans to reopen many new activities, including restaurant dining and shopping at malls.

But there are signs that counties will have to scramble at times to stifle outbreaks. In Butte County, a church held a Mother's Day service with 180 attendees in defiance of the governor's order prohibiting large groups. One attendee subsequently tested positive for COVID-19, forcing the county health team to attempt to contact everyone who was at the service.

Butte County officials this week refused to discuss how that effort went. But, in an indication that the county may be struggling, the county's health director, who oversees outbreaks and contact tracing, submitted his resignation last week. The county has declined comment. The Sacramento Bee has submitted Public Records Act requests seeking more information.

The incident serves as a warning. Everyone in the health world is "scrambling" to understand the virus, get organized and get ahead of it, said disease control expert Marx of Johns Hopkins University.

"Just the sheer number of cases and the sheer urgency of getting to cases before they transmit to other people is unprecedented," she said. "We should have been doing this (mobilizing tracers) in March.

"We would have been ready. But better late than never."

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The contact tracing effort, if successful, will be a remarkable example of regional and public-academia cooperation.

In April, as California ramped up its testing capacity in communities, it more quietly turned to the University of California, San Francisco to create an online training program that could turn county workers, new hires and some volunteers into contact tracers with 20 hours of education.

That program, co-managed by UCLA, has already begun training and graduating tracers and is expected to step up its pace this week. State health officials have not disclosed, however, how many people they expect to see trained by week's end.

UCLA extension program Dean Eric Bullard is helping run what he calls a COVID-19 training academy.

"They're learning basic principles of public health and epidemiology, then case investigation and contact tracing," Bullard said. "Then cultural sensitivity and confidentiality, involving role playing, interviewing skills, working with diverse populations."

The effort is creating what may be the fastest-rising occupation in the state. San Diego County is advertising now for temporary contact tracers, offering $19.50 an hour (the equivalent of $40,000 a year full time). Other counties have issued help wanted ads.

The job could be lucrative in the long run. In Shasta County, a disease specialist at the top end of scale can make up to $70,000. In Sacramento County, a senior communicable disease investigator can make $66,000.

"We see this as a rolling workforce" over the next couple of years, UCLA's Bullard said. "As the librarians return to (their former) work, we need to train new people. It's an emerging paid workforce in California."

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Vaughn, Yolo County's public health director, called contact tracers the "workhorses." His county has quickly ramped up to 37 people capable of the work.

The job starts the moment the county is notified of a positive test. A case investigator, generally a health officer with medical knowledge, calls or visits infected individuals and pushes them to recall where they went and who they dealt with, starting about two days before symptoms began to show.

The investigator may ask the person to check their calendar, even their bank account, to remind them of where they were and who they may have exposed - the person in the next cubicle at work, a carpool partner, a fellow basketball or bridge player, their roommates or family.

They skip, however, people the person may have had passing contact with. "Going through the grocery store, that's pretty low risk of exposing others," Vaughn said. "We're not going to notify the store because the risk is low."

The same goes at the workplace. If the infected person leaned over a co-worker's shoulder for 10 minutes discussing a power point presentation on the computer, that person will be called. If other co-workers were at desks elsewhere in the room and rarely passed within 6 feet of the infected person, no.

Tracers don't disclose the name of the infected person. But often, the recipient of the call knows who it is. "It's not often it's a complete stranger," Vaughn said.

Health officers are empowered to compel people to isolate or quarantine at home, but for now, counties are counting on people using common sense and compassion.

Yolo County hasn't had an issue with an infected person openly disregarding the request, Vaughn said. "We're not monitoring every day, we're not tracking them, a lot of it is the honor system."

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It's yet to be seen how well this new industry will fare when dealing with the elevated level of fear, confusion and governmental distrust that surrounds the pandemic.

Some residents at a recent Placer County board of supervisors meeting expressed anger at the mere thought of contact tracing, seeing it as a way for the government to invade their privacy and keep tabs on them.

"I am not going to submit to contact tracing, and I'm not going to get tested, and I'm not going to get vaccinations," one caller told the Placer County supervisors. "We are a free people."

Some of the mistrust may be due to news reports about technology companies Apple and Google pitching cellphone apps that local governments can use to track people who are willing to use the app. In South Korea, the tracking system is not voluntary. The government tracks where people are via their phones and buzzes them when they are near a person known to be infected.

Andrew Noymer, an associate public health professor at the University of California, Irvine who has emerged as a leading voice on government response to the virus, suggests that may be the wrong track.

On paper, a Bluetooth-based app that notifies a user they've been near someone who tested positive could help stem an outbreak, Noymer said. But he's skeptical. It's unclear how sensitive or accurate the tracking would be and how people without access to smartphones would be able to benefit from it.

"I do think the privacy, the encroachment, concerns are nothing to be dismissed out of hand," he added.

In California, officials are pitching contact tracing as far more benign and personal than that, casting tracers as people who help keep you and your family, friends and co-workers safe.

Placer County's public health epidemiologist April Holland said she doesn't see her county dealing with tracking apps. "I think we're going to stick to the gumshoe method and go person by person," she said.

However, people still get nervous when a government employee calls them out of the blue, said Dr. Homer Rice, who oversees contract tracers for Yuba and Sutter counties.

Some people he calls don't believe him. They think he's a scammer. Others don't want to hear that they may be infected. He's been hung up on. Others tell him to mind his own business when he asks questions, such as how they are feeling. "You don't need to know that!" one adamant person said.

"We're really just trying to help people," he said. "We (recently) caught a whole family that tested positive. Some in the family didn't have any symptoms. They would have been going to the store.

"Knowing we got that family isolated, so they didn't go out, you're like, 'Whew. Yeah. I did my job today.'"

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Johns Hopkins University health professor Marx, who acts as a coronavirus outreach consultant to the city of Baltimore, said contact tracers are not the definitive backstop that some might present them to be.

They can have trouble communicating with or even reaching people who are distrustful of government, who are culturally sequestered from mainstream society or who are homeless. Communities can better help their residents by reaching out to leaders who are trusted in underserved communities to act as intermediaries.

Communities should also set up call centers, so that people in need or with questions can reach out to county health departments, rather than hear nothing until the day a contact tracer calls with potential bad news. "The word hasn't gotten out as well as it should to communities of highest risk," Marx said.

She sees a thin silver lining though for community health. The rapid-fire hiring of what likely will be hundreds of thousands of contact tracers across the United States is a first step toward belatedly compensating for years of under-funding public health offices both locally and nationally.

"It would be great if some of these people can continue to work in public health and fill holes," she said.

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