(CNN) While President Donald Trump's May 1 deadline to reopen parts of the economy looms, state and local government officials, along with public health experts, are calling for contact tracing teams to start tracking coronavirus positive patients to both contain the virus and start reopening some businesses.

But with only two weeks to go, many parts of the country don't have contact tracing teams that are up to speed enough to reopen places, according to experts.

Contact tracing is a widely used method in public health that relies on identifying every person who tests positive with an infection, isolating them, and then finding anyone that person could have infected. These contacts may then be quarantined before they can spread the virus to others. It's a tedious approach, but one widely credited with stopping SARS in 2004, after that coronavirus outbreak infected nearly 8,000 people and killed close to 800 of them.

With government officials, business owners and people out of work concerned about the impact of long-term social distancing measures on the economy, public health officials say contact tracing is a necessary step needed before certain businesses can reopen and people can start to return normal activities.

Trump unveiled a three-phase return-to-normal plan to all 50 state governors on Thursday. It outlines steps each state should take once they meet a certain threshold for number of cases declining over two weeks and certain level of capacity and ability to care for all patients in hospitals. The 17-page document makes a brief mention of contact tracing, saying states should have the ability to do it, but does not offer guidance on how to do it, how many people will be needed to do it, or explain how the federal government will help build up contact tracing systems.

Many experts believe the US is nowhere near where it needs to be in its ability to contact trace Covid-positive people and those they've been in contact with. Other countries, like South Korea , have found contact tracing to be an effective method to contain their coronavirus outbreak.

More public health workers needed, experts say

study released by Johns Hopkins University last week estimates that the US needs at least 100,000 additional public health workers to assist with large-scale contact tracing efforts before a robust system can begin operating nationwide.

Anita Cicero, the deputy director at the Johns Hopkins Center for Health Security and a co-author of the study, said that the US will likely need more than 100,000, but the initial number is a good start to get contact tracing started in some of the more heavily impacted areas.

"We're not saying that that is the upper limit of what would be needed but we knew that it's, you know, it's a pretty ambitious goal," Cicero told CNN in a phone interview. "If we can start with that, then people could be added if needed or scaled back."

Cicero said Hopkins decided to do the study to point out what resources would be needed to effectively contact trace across the country.

"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. "So, we felt that it was important to highlight that as a critical gap and try to quantify how shorthanded are we for the contact tracing workforce."

While 100,000 additional public health workers may seem like a large number, the study points out per capita, "it is still the equivalent of less than half the number employed in Wuhan City," where the coronavirus outbreak began months ago in China.

In a report released Friday, former Centers for Disease Control and Prevention Director Dr. Tom Frieden said the need could reach "several hundred thousand."

George Rutherford, an epidemiology professor at the University of California at San Francisco who is working on San Francisco's contact tracing program, said he believes the country probably needs closer to 300,000 public health workers to focus on contact tracing full-time.

"It has to be an absolute pillar of the response going forward. If we can get the case counts down ... to a manageable number, contact tracing is a far cleaner, far more surgical solution to keeping transmission low than really anything else at our disposal in this country," Rutherford told CNN.

But Rutherford said the US is "not at all" ready to reach that level. "We don't have enough people to do it," he said.

Rutherford noted that some who are out of work are being trained to work on San Francisco's program. While the recently unemployed workforce is a good source of people to pull from to staff these projects, it will take time to get people hired and trained to do contact tracing work, he said.

The Hopkins study estimated that Congress "will need to appropriate approximately $3.6 billion in emergency funding to state and territorial health departments," to ramp up contact tracing and pay people to do the work needed.

Contact tracing efforts ramp up in Massachusetts and San Francisco

In response to the coming need, some cities and states have started developing contact tracing systems of their own, like Rutherford's program in San Francisco. In about two weeks, San Francisco went from having only 10 people in the city's public health department working on contact tracing to about 150 people, Rutherford said.

The city government and public health department partnered with University of California San Francisco to start a contact tracing program for the city. Rutherford led a group of public health professionals from UCSF that normally work overseas but whose projects are now on hold due to the pandemic to get them trained and working on the city's contact tracing efforts. UCSF staff are trained public health professionals, so they were able to get up to speed quickly, he said.

Registered nurse Raquel Hernandez reaches in to swab a passenger for a Covid-19 test at a mobile testing site in Sulphur, Oklahoma, on Tuesday, April 14, 2020.

Rutherford said they developed a training program with the city's Department of Health and a local CDC training center in the Bay area. After training UCSF staff, Rutherford and city officials started looking for more people they could recruit to work on the program. They called on other city employees who had been furloughed to get trained. Now, they are training a group of librarians and city attorneys to become volunteer contact tracers as well.

"It's a personnel-intense activity," Rutherford said. "I think volunteers are great, but you've got to have paid staff too."

The volunteers are largely doing email, phone call and texting work remotely to keep track of people who have tested positive or come into contact with someone who has tested positive, while public health professionals manage more high-risk, in-person contact when necessary.

Massachusetts started a state-wide contact tracing initiative at the beginning of April, contracting with Partners In Health , a Boston-based non-profit organization that focuses on global public health issues. The Community Tracing Collaborative aims to hire 1,000 contact tracers to track contacts of all Covid-19 positive patients across the state and to support individuals in quarantine.

"We need to have a very significant contact tracing program in place," Massachusetts Gov. Charlie Baker said at a news conference. "From our point of view, that is a must-do with respect to anything that looks like a reopening of the commonwealth or a move towards reopening the economy. "

Partners In Health has a team of more than 200 people working on the contact tracing program, continuing to hire until they reach 1,000 employees. After Baker announced the collaboration on April 3, Dr. Joia Mukherjee, the non-profit's chief medical officer, said they received more than 900 applicants in 72 hours.

More tests will be needed to conduct contact tracing

While the contact tracing efforts in Massachusetts are a positive step, public health experts warn that the program won't be completely effective without a huge increase in testing capabilities along with the development of contact tracing systems.

"We're here to do the contact tracing, but we don't have tests. If I could scream as loud as I could, we need tests. Our area in the state has been the last to really get the attention it needs," Nancy Paull, CEO of SSTAR, an integrated primary and behavioral health care organization in Massachusetts, told CNN.

Paull's center has started a contact tracing team in Falls River, an economically depressed area with a large homeless population in the state's southeast region.

Dr. Ranu Dhillon, a researcher with the Division of Global Health Equity at Brigham and Women's Hospital in Boston and an instructor at Harvard Medical School, said that the US's testing capabilities are nowhere near where they need to be if contact tracing is to work properly.

"Based on the testing capacity we have, for example, to do something like that in New York City, there's like 8 million people in New York City. We need 8 million tests. Right now, we do about 150,000 a day," Dhillon told CNN in a phone interview. "We're orders of magnitude away from what we need to be, not that we shouldn't continue to strive to get there."

Dhillon pointed out there are still many people who are asymptomatic but have been infected with Covid-19. Without widespread testing, such people could also spread the virus.

While testing capacity is an issue, those hired for the contact tracing program in Massachusetts are separated into three types of personnel: case investigators, contact tracers and care resource managers. Mukherjee said all positions are remote and those selected are trained in two days by webinar and an interactive session, a program created in tandem by Partners in Health and the state government.

All contact is made by phone. Case investigators contact the newly diagnosed to identify who they've been within six feet of, for more than 15 minutes, in the last 14 days. A contact tracer calls each of those individuals to let them know they might have been exposed. The contact tracers ask how the potentially exposed person is feeling and if they have symptoms. They may also advise on needed medical care and help people figure out how to self-quarantine.

If people are unable to quarantine safely because they live in a multi-generational home or don't have access to their own bathroom among other issues, they are then referred to a resource manager who helps them find a place to safely self-isolate or provide them with resources to do so.

"Our work around the world has taught us that privilege and economic means allow you to be able to do things that people who are poor and more vulnerable can't do," Mukherjee told CNN.

CDC starts contact tracing pilot program in 8 states

This week, the CDC started a pilot program, sending community protection teams to eight states to ramp up contact tracing efforts, according to a federal health official with knowledge of the program. The teams will be sent to New Mexico, Wyoming, Idaho, Alaska, North Dakota, Kentucky, West Virginia and Ohio.

The teams will be "testing new technologies," like applications and mobile technology for contact tracing, as well as "having people do self-swabbing and evaluating how effective that is," the official told CNN. The teams will work directly with state and local health departments to support epidemiologists and labs.

The CDC often deploys teams to major public health emergencies both in the US and abroad. In 2016, the CDC's Global Rapid Response Team sent health, communications and logistics experts to 90 public health crises in the US and around the world, including outbreaks of Ebola, polio, yellow fever and cholera.

The teams can deploy on short notice and can remain in the field for months to stop health threats or to limit health threats from becoming a bigger issue.