Instead, states and cities are opting to hire thousands of public health workers who will have to carry out the laborious task of phoning everyone with a confirmed case.

They'll want to know, in turn, everyone that the patient came into close contact with -- defined as less than six feet (two meters) -- for 15 minutes or longer. These people will then be called and asked to self-quarantine. 

It's painstaking work that can complement the opt-in mobile phone based contact tracing, announced by Apple and Google recently. The investigators, who don't require medical training, work from home, using computer software, and each call takes at least half an hour.

Massachusetts was the first to launch its program at the start of April, announcing it would recruit 1,000 contact tracers (17,000 have applied). San Francisco has announced a similar initiative, and other states and jurisdictions are also starting up.

"It's late," said Dr Joia Mukherjee, chief medical officer of Partners in Health, the nonprofit chosen by Massachusetts to manage its program. "It would have been easier to do it after the first case."

But it's still possible to catch up, she said. "All epidemics are highly localized. If we look at the top line numbers, everyone just gets terrified. But it's town by town, block by block, and city by city."

"If we can do it in a place like Liberia, how is it that we couldn't do it in Massachusetts?" added Mukherjee.

In Africa and other parts of the world this type of work is considered one of the founding principles of public health. 

But, said Mukherjee, "for 40 years, the US has disinvested in public health and community health in favor of hospitals, and the sort of things that generate revenue."

100,000 agents 

In Wuhan, 1,800 teams of five people carried out this work, often voluntarily. Scaling that up to the US outbreak would mean 265,000 people are needed.

Researchers at Johns Hopkins University suggested 100,000 to begin with "to assist with the enormous and unprecedented task of contact investigation and containment on this scale."

The country currently has, at most, only 5,000 specialists responsible for monitoring cases of communicable diseases such as HIV or tuberculosis, Michael Fraser, head of the Association of State and Territorial Health Officials (ASTHO) told AFP.

He doesn't expect recruiting to start before two to four weeks in most states.

"Our goal is to get this in place for the reopening," he said.

It was not until Monday that the White House, through Vice President Mike Pence, announced the dispatch of reinforcements from the Centers for Disease Control and Prevention (CDC) to each state.

In an email to AFP, the CDC said it had deployed 24 teams to each state, with over 600 staff nationwide.

But states like Texas plan to start easing their lockdown orders over the coming days, reopening some shops and businesses. 

The Lone Star state, home to almost 30 million people, would need at least 8,000 contact tracers, estimates ASTHO. 

"There's definitely going to be some risks" associated with lifting social distancing orders without having the right surveillance mechanisms in place, warned Fraser. 

That's to say nothing of the need to ramp up contact tracing as more and more societal activities resume. 

In the absence of enough personnel, more at-risk groups like nursing homes, hospitals and vulnerable populations should be prioritized.

When people get called in Massachusetts, the state has come to an agreement with telecoms operators to display "Covid Care Team" on the Caller ID, to try to maximize the number of people who pick up.

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