clock menu more-arrow no yes mobile
Zac Freeland/Vox

Filed under:

Contact tracing, explained

The US needs tens of thousands of “disease detectives” to safely reopen the economy.

Dylan Scott covers health care for Vox. He has reported on health policy for more than 10 years, writing for Governing magazine, Talking Points Memo and STAT before joining Vox in 2017.

To safely begin reopening the economy, America will need to rely on so-called disease detectives to track the novel coronavirus and contain new emerging outbreaks before they grow out of control.

This work, known as “contact tracing,” is critical for state plans to relax social distancing without inviting a sudden resurgence of Covid-19 cases. All the various plans to ease social distancing restrictions rely on this work.

To prevent another spike in cases, public health workers will perform the difficult and sometimes tedious process of interviewing people diagnosed with Covid-19, finding out whom they have recently been in close physical contact with, and then informing those people of their potential exposure and advising them to self-isolate and get tested.

“The rapidity with which this work has to be done is really unprecedented,” Jeff Duchin, who leads the epidemiology division in King County, Washington, the first epicenter of the pandemic in the United States, told me. “If you miss a few cases, those little sparks can set off a forest fire.”

People in this field — officially known as disease intervention specialists — were previously focused on HIV and other sexually transmitted infections. Tracing Covid-19 presents new challenges. One person infected with the virus can spread it to half a dozen others and symptoms often don’t present themselves for days after a person is already contagious.

New technology could assist public health workers with their jobs. Apple and Google are reengineering smartphones’ Bluetooth functions so they could silently and anonymously track the people each of us comes into close contact with. But those sci-fi public health ventures have problems, both in safeguarding privacy and convincing people to use them.

That leaves old-fashioned disease detecting as one of the best tools available to track Covid-19 once people start going back to work and out in public places. But the fear is the US won’t have enough people to do this on the necessary scale. Researchers say the country is going to need tens of thousands more workers — and billions of dollars — to handle the contact tracing workload expected for the coronavirus.

The disease intervention specialists I spoke with said they haven’t been overwhelmed to date — but they’ve been working in a lockdown situation, with most people’s contacts limited to whomever they live with. Once more people start going back to school and work, the job will become much harder.

“It’s going to be very challenging,” Duchin said. “We’re not absolutely sure that we’re gonna be able to do it.”

How public health “detectives” track diseases like Covid-19

John Owens Jr. has been a disease intervention specialist in Rochester, New York, for 20 years. He now supervises the contact tracing team there. His phone rings twice in five minutes when we talk. “My phone never stops ringing.”

Before the coronavirus showed up, his team was tracking HIV, syphilis, gonorrhea, and chlamydia. One person on the contact tracing squad would receive maybe three or four people every day. They would go interview a person who tested positive for these diseases and find out who their recent sexual partners had been. The disease intervention specialist would then get contact information for those people and notify them of their potential exposure. Depending on the number of contacts — and there could be anywhere from one or two to 30 — it could take mere hours or nearly a week to complete that process.

“Being able to gain rapport with people quickly, that is the single most important thing,” Owens said. “if you are good at that, you will be good at this.”

But Owens and his team had never tracked a disease quite like Covid-19 before; the only remotely comparable experience was a past measles outbreak. They’re dealing with a lot of calls: 40 cases or so every day for his team of eight to 10 workers, depending on the day.

A respiratory virus like SARS-Cov-2 is also much harder to track than a sexually transmitted infection. The disease intervention team has to ask patients about everybody they’ve been in close proximity to since two days before they first felt symptoms from the coronavirus.

“You can’t ever really know how you got it or when you got it,” Owens said. “It is much more challenging. It’s much easier to figure it out with STDs or HIV.”

On the other hand, the contact tracing workers I spoke with said people are usually more forthcoming when talking about Covid-19 than they are when discussing their recent sexual history.

Dr. Daniel Kombert works with other medical professionals as they answer calls and track data at the Hartford HealthCare Covid-19 command center in Newington, Connecticut, on March 10.
Kassi Jackson/Hartford Courant/Tribune News Service/Getty Images

“People are dealing with the anxiety of ‘Who have I infected?,’” Bryana Fryczynski, a disease intervention specialist with the Michigan state health department, told me. “People are having to deal with those emotions while being isolated. We take that burden away. They know at the end of that conversation, we have the information we need and they can rest easily.”

Both Owens and Fryczynski said their work had been made simpler by the lockdowns in place all over the country; people don’t have many contacts except their immediate family members or roommates.

They expect that to change — the number of contacts to increase, the work of tracing the disease to become more difficult — as the stay-at-home restrictions ease. Michigan is in a political fight right now over rolling back some social distancing rules. Things are changing all the time, and there are no typical days with this job.

Owens remembered in the early days of the pandemic, people were getting exposed at churches; others had gotten the virus in cafeterias and bowling alleys. It’s asking a lot of people, to try to remember anybody they’ve been physically within 6 feet of for a period of 15 minutes or more. And it’s going to be more difficult as people start going to offices or restaurants again.

“I think things will change as places start to slowly reopen,” Fryczynski said. “For now, people are like, ‘It’s the people in my household.’”

Phone apps could help with contact tracing — but they have shortcomings

There has been a hope that, as people start venturing back out into the world, our smartphones can help automate some of the work contact tracing teams are asked to do. In April, Apple and Google rolled out a plan for adapting Bluetooth functionality to keep track of our contacts, as Recode’s Adam Clark Estes and Shirin Ghaffary explained:

The contact-tracing tool Apple and Google want to create would have your smartphone log when you’ve come into close contact with other people. If one of those people later reports Covid-19 symptoms to a public health authority, your phone would receive an alert about the diagnosis. It works a bit like exchanging contact information with everyone you meet, except everything is designed to be anonymous and automatic.

Once it’s equipped with this new contact-tracing software, your smartphone will periodically exchange anonymized tracing keys with nearby devices via Bluetooth. The phone maintains a list of keys collected from people you have come in contact that with stays on your device, not a server, unless you test positive for coronavirus and report your diagnosis. If that happens, your phone will then upload those keys to a server that will send alerts to the owners of recently collected keys. The alert will not reveal who’s infected — in this example, that’s you — but it will share information for what people who were in proximity to you should do next.

This naturally raises a lot of privacy concerns for Americans. While policy experts have suggested ways to build public trust in these apps, a recent Washington Post-University of Maryland poll found about 60 percent of Americans either would not or could not allow their phone to silently and anonymously surveil them, even in the name of public health. Smartphone users were roughly split down the middle, 50-50. Another 1 in 6 Americans don’t have a smartphone with the capability to run the kind of app Apple and Google envisioned.

North Dakota went ahead and set up its own contact tracing app, asking people to download it to help with the effort to track Covid-19. But only 3 percent of the state, about 25,000 people, had done so as of April 29, according to the New York Times.

For context, Oxford researchers have estimated governments would need more like 60 percent of their citizens to participate for these apps to be effective.

The logo of a tracking app being used in Germany.
Thomas Trutschel/Photothek/Getty Images
Another Covid-19 tracking app being used in Germany.
Thomas Trutschel/Photothek/Getty Images

To be fair, this is not only a problem for the US. Other countries have failed to achieve the necessary buy-in from their citizens, too, as Gaffary wrote for Recode. Just 20 percent of Singapore’s population has downloaded its tracing app; Norway has done a little better, reaching 30 percent in the first week, but the government must still double that to reach the necessary market saturation.

Without a sudden uptick in people willing to use a smartphone app to aid contact tracing in the US, the traditional work of disease intervention specialists is going to be critical to the Covid-19 response.

But experts don’t think the US has nearly enough people trained to do that work right now.

We need a lot more people to do this contact tracing work

Before the pandemic exploded, state and local health departments had about 2,000 workers doing contact tracing. The varying estimates for how many people are needed to trace Covid-19 are all exponentially larger than that.

The Johns Hopkins Center for Health Security estimated the US needs 100,000 people performing this work for state and local agencies. Former Centers for Disease Control and Prevention Director Tom Frieden told Politico the necessary number of workers could be as high as 300,000.

Money is going to be the problem. The Johns Hopkins researchers thought it would take $3.6 billion to hire and train enough people to expand the disease intervention ranks, a figure endorsed by the Association of State and Territorial Health Officials. But state budgets are squeezed, and while people could in theory volunteer for these jobs, there is also record unemployment right now. It makes a lot of sense to put out-of-work people, or people training to work in the medical fields, on these assignments — and to pay them. But state governments would need financial help from Congress to do it.

The most recent stimulus bill put aside $11 billion for state and local health programs, but that was supposed to cover testing and other activities as well as contact tracing. More money will be needed, especially if the people like Frieden are right and we need more like 300,000 people to perform this job to keep the coronavirus contained.

In the meantime, states and cities are doing what they can to expand the tracing capacity. California has put librarians and attorneys to work interviewing people and calling contacts. New York Gov. Andrew Cuomo announced he was partnering with former NYC Mayor Mike Bloomberg’s philanthropic group, as well as Johns Hopkins University, to train people to do contact tracing. Maryland signed a contract with NORC-University of Chicago to quadruple its contact tracing capabilities, enough to track as many as 1,000 new cases per day. (Right now, the state is seeing a little less than that, between 600 and 900 in recent days.)

New York Gov. Andrew Cuomo speaks with Mike Bloomberg on video about contact tracing during a press conference, on April 30.
Michael Brochstein/Echoes Wire/Barcroft Media/Getty Images

And it still might not be enough to prevent future waves and the need to reinstitute stricter social distancing rules. Public health experts keep cautioning lockdowns may need to be reinstated if there is a rapid rise in cases and hospitalizations that risks overwhelming local health care systems.

“I tend to be somewhat on the pessimistic side about contact tracing as a general control strategy. What we are pretty sure about is that contact tracing works well when you have relatively few cases, you have the resources to do it and when you have even fewer cases that are unknown,” Marc Lipsitch, a Harvard University epidemiologist, told reporters on a recent call. “Neither of those is true right now in most parts of the United States.”

Nevertheless, the more people who can do the work, the more it can help. Owens told me Rochester has “so many volunteers” who want to come and help. In Michigan, Fryczynski said state health department workers are being assigned to assist the cities and counties that are facing an overwhelming load of Covid-19 cases.

“Right now, it’s an all-hands-on-deck situation.”

Eliza Barclay contributed to this report.

Future Perfect

Should Big Pharma pay poor countries for finding new diseases?


Can Biden contain the fallout from his Gaza policy in Michigan?


Do 1 in 5 Americans really believe Taylor Swift is in cahoots with Biden?

View all stories in Politics

Sign up for the newsletter Today, Explained

Understand the world with a daily explainer plus the most compelling stories of the day.