When a strange new virus begins spreading through a community, state and local health departments know who to call: The contact tracers.

They are the men and women who meticulously track down the friends, family and colleagues of infected people to warn them they’re in danger and urge them to quarantine.

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By the time the novel coronavirus was detected in Louisiana in early March, it was already too late. The virus was simply too widespread to find and isolate everyone who might have contracted it, experts say.

Louisiana is still recording dozens of deaths from the coronavirus every day, but there are some encouraging signs, like dropping hospitalization rates. As Louisiana Gov. John Bel Edwards and other leaders plan for the moment when they can reopen their economies, they may rely on a vast new army of contact tracers to squash future outbreaks. Louisiana hasn’t announced its plans, but public health experts say that up to 100,000 contact tracers could be needed nationwide to guard against COVID-19.

While far more attention has been paid thus far to the lack of widespread and timely testing, epidemiologists say tests should be complemented by contact tracing to keep future coronavirus sparks from turning into forest fires.

“We’re going to need a whole giant cadre of people,” said Gavin Yamey, a global health professor at Duke University. “If we take our foot off the gas, and we don’t have really great ability to test people to get a rapid result to isolate people, and to do contact tracing, this thing is going to come back with a vengeance.”

Contact tracing is laborious, time-consuming work. Tracers interview infected people to come up with a list of everyone they’ve interacted with when they were infectious, attempting to gather details like how long they were in contact and how closely.

In Louisiana, contact tracing has been used in recent years to stem the spread of infections like syphilis. Health officials track down the sexual partners of patients with syphilis and urge them to seek treatment.

With coronavirus, the key next step is urging people who have come into contact with carriers to self-quarantine or seek medical help if needed, said Josh Michaud, an associate director for global health policy at the Kaiser Family Foundation.

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“It’s something that public health departments have been using for over 100 years,” he said. “The idea behind it is if you can identify most or all of the people who have a particular disease, then you can remove those people from circulation and prevent them from continuing the transmission chain.”

The peculiar qualities that have made the novel coronavirus so contagious also make it harder to trace, however. Infected people can spread the disease even before they begin to exhibit symptoms, giving them days to pass on the virus without knowing it.

South Korea and Singapore have used high-tech tools like cell phone data and surveillance footage to aid contact tracers and effectively nip the coronavirus in the bud.

But Louisiana, like many other states, appears to have been caught so off guard that contact tracing quickly became ineffective.

The state attempted wholesale contact tracing for “a couple weeks” after the first coronavirus case was confirmed on March 9, said Susanne Straif-Bourgeois, an assistant professor at LSU Health Sciences Center New Orleans who spent years as the assistant state epidemiologist.

“They were very busy, because basically at that point for every case which was confirmed you have to go 14 days back and see how they potentially exposed other people,” she said. “That’s a long time, and at that point everything was more or less ‘normal,’ so potentially a lot of people could’ve been exposed to that infected person.”

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By the end of March, the coronavirus was so widespread in New Orleans that officials had narrowed their contact tracing in the metro area to focus on vulnerable populations. The state was right to switch tactics then, Straif-Bourgeois said. The problem at that point was so big that only a blunt tool like a stay-home order would work.

“Contact tracing is especially effective early on in an epidemic when there aren’t that many cases and you can feel confident that you’ve identified most of the cases,” Michaud said. But when the case count is growing exponentially, contact tracers will only be able to stop a “sliver” of the transmission chains, he added.

Nevertheless, the Louisiana Department of Health said it is investigating individual cases and conducting contact tracing everywhere outside the greater New Orleans area.

The state has about 30 infectious disease epidemiologists. About 75 additional Louisiana Department of Health employees, including public health nurses and epidemiologists in other programs, have been re-directed to case investigation and contact tracing, according to Aly Neel, a department spokeswoman.

Local officials have provided help when they can, but their limited resources have also been overwhelmed by the tidal wave of coronavirus cases.

The New Orleans Health Department has assisted the state with contact tracing when possible, according to a City Hall spokesman.

“We are looking at ways to increase contact tracing over the next few weeks as our rate of new cases slows and we plan for easing current mandates,” said spokesman Trey Caruso. “We are currently discussing ways to engage healthcare providers, our Medical Reserve Corps volunteers and community partners in these efforts.”

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Orleans is the only parish with its own dedicated health department. In Jefferson Parish, which had the second-highest number of Covid-19 deaths through Friday, all contact tracing has been handled by the state.

In the future, the state Department of Health said it plans to adapt its contact tracing tactics as the coronavirus curve — hopefully — continues to flatten.

“We are looking at the role of both the state and private sectors working in partnership to expand our contact tracing capacity to the level needed to suppress the outbreak going forward,” Neel said.

Rebekah Gee, a former health secretary under Gov. Edwards, said medical students and other volunteers might be able to help.

“The Louisiana Public Health Department has some really dedicated people in it — but there are way too few of them, particularly in infectious disease,” said Susan Hassig, an epidemiology professor at Tulane University. “They’ve been working really hard but it’s like trying to swim up Niagara Falls.”

Other states are relying on volunteers, retrained government employees and fresh hires to do contact tracing. Massachusetts is teaming up with the non-profit Partners in Health, which is better known for its work in Haiti, to hire 1,000 contact tracers. Utah is retraining hundreds of state workers.

The federal Centers for Disease Control and Prevention is also planning to bulk up its corps of contact tracers, although the agency hasn’t given specifics yet. Meanwhile, tech giants like Apple and Google are teaming up to develop an app with the aim of warning users when they’ve come into contact with infected people, though they are trying to do so while still protecting privacy.

In an April 10 report, officials at the Johns Hopkins Center for Health Security and Association of State and Territorial Health Officials urged the federal government to direct hiring through the local health departments that are already on the front line fighting against coronavirus.

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Many state and local public health departments saw cuts during the last economic downturn, according to the report. The officials urged the federal government to dedicate $3.6 billion for states to hire 100,000 contact tracers at $17 an hour.

“This is a win-win,” said Marcus Plescia, chief medical officer at the Association of State and Territorial Health Officials. “People need work, and this is work we can train people up for pretty quickly where they can be employed again.”

Staff writer Bryn Stole contributed to this report.