How contact tracing slows the spread of COVID-19

By Emily Stifler Wolfe, Montana Free Press

BOZEMAN — Adam woke up with a fever on the morning of Tuesday, February 25. His body ached and his sheets were soaked with sweat. He called in sick to work, and his girlfriend drove him to the viral triage clinic at Bozeman Health Deaconess Hospital.

There, nurses asked about his symptoms and, because he didn’t meet testing criteria for COVID-19, they swabbed him for the flu. A doctor called when his flu test came back negative later that day.

“They told me, ‘Assume you have [COVID-19], tell the people you’ve been with you might have it, and suggest they quarantine.’” They sent his swab to the state lab for testing, and two days later his results came back positive.

Adam (who requested anonymity to protect his privacy and that of his employer) is 29 and had no pre-existing conditions. He had self-isolated and was feeling better by the time a public health nurse from the Gallatin City-County Health Department called to ask about his close contacts, explaining that meant people who’d been within arm’s reach for more than 10 minutes. The list: his girlfriend, his roommate, and two coworkers.

The nurse called his coworkers and asked about symptoms, instructing one who’d driven in a vehicle with Adam the day before he fell ill to quarantine for 14 days. The other coworker had been in a meeting with Adam but sat at a distance; the nurse said he didn’t need to quarantine but should monitor himself closely. Adam’s roommate had developed symptoms around the same time as Adam and was already in self-isolation, as was Adam’s girlfriend, who got sick a week after he did. The roommates think they contracted the virus from a mutual friend, whom they’d both seen after he flew home from a international work trip via Amsterdam.

“As far as I know, it stopped with my girlfriend,” Adam said.

This is how contact tracing, the public health method used to slow communicable disease spread, is supposed to work. Once public health officials identify a case, they isolate the infected person and quarantine anyone who’s been in close contact with them, interrupting the chain of transmission.

It also illustrates a particular challenge of trying to trace the novel coronavirus: By the time Adam and his roommate were ill, their friend who’d traveled abroad was already in southern Utah on vacation. Neither he nor the people he was traveling with showed symptoms, so it’s possible he never had the virus, was no longer contagious, or may have been an asymptomatic carrier.

Contact tracing, combined with several other public health tools, is the most effective means of slowing the outbreak, said Jim Murphy, the epidemiologist and chief of Montana’s Communicable Disease and Prevention Bureau.

“The things we have, we’re using,” Murphy said, listing testing, social distancing, quarantine and isolation for sick and exposed people, personal protective equipment for health care workers, and masks for the public. “What we are missing in a perfect world would be [a] prophylaxis, effective medication that could be used to treat somebody that’s at the highest risk of complications, and of course a vaccine.”

On April 16, the White House released guidelines for “Opening Up America Again.” But national public health officials say before the stay-at-home orders in place across much of the country can be lifted, a robust system for contact tracing will need to be in place to allow for effective intervention if case numbers begin to rise again. Some experts estimate that will require between 100,000 and 300,000 people doing the investigations nationwide.

Right now in Montana, social distancing efforts have been effective, Murphy said, and the state needs to be prepared for an inevitable spike in cases when the state’s stay-at-home order is lifted. That means having capacity for rigorous contact tracing, plus expanded supplies of test kits and medical protective equipment.

“Before you can say, ‘Oh yeah, let’s turn all those measures off, let’s go back to normal,’ you would want to make sure you have all those resources in the cabinets, ready to go, in case that backfires.”

Otherwise, Murphy said, the state will “go right back to closing everything down again.”

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Contact investigations are nothing new. Even before COVID-19, health departments already spent a large portion of their time tracking potential vectors for about 40 different communicable conditions and diseases, including pertussis, tuberculosis and HIV. Contact tracing ended smallpox and helped control Ebola.

“It’s what we do every day,” said Cindi Spinelli, the communicable disease and immunization program manager at the Gallatin City-County Public Health Department, which is dealing with Montana’s largest COVID-19 outbreak, totalling 142, or a third of the state’s 422 cases, as of April 17.

“Because Montana and Gallatin County had restrictions in place early, we have been really lucky in terms of contact tracing,” Spinelli said. “It is mostly household members and family members. When the restrictions are lifted, this will change, and we are preparing for that now.”

“Some people have a lot of stories to tell you, and they will go into the weeds about going to the vet or wherever they went. … You have to let them verbalize all that, and try to bring them around to the important questions.” 

—Carbon County public health nurse Roberta Cady

The department added 10 core people to help with the investigations, and trained seven of its sanitarians to work in the COVID-19 call center, Spinelli said. Three retired nurses and two medical students have volunteered to answer the phones there, now with help from Bozeman Health staff nurses.

In Wuhan, China, where the outbreak began, more than 9,000 public health workers traced tens of thousands of people a day, according to the World Health Organization, ultimately slowing the disease’s rapid spread. South Korea used meticulous contact investigations combined with widespread testing to curb its outbreak.

And while there is a national shortage of test kits, Murphy said, “testing has not been our limitation in Montana.” Blanket testing, he said, would provide only limited actionable information.

“Testing everybody would provide you a snapshot at one bit of time. … We’d have to test people literally every three days to have that be a viable strategy. Nobody’s really promoting anything like that.”

What does work, he said, is testing people who are symptomatic and then following up with rigorous contact tracing.

These efforts are labor-intensive, according to Murphy.

“There’s a lot of things that are involved in COVID response, even in the absence of cases in your jurisdiction,” Murphy said, listing public messaging, fielding questions, and addressing suspected cases. “Then when an actual case happens, the hard work starts, trying to figure out who may have been at risk through contact investigations.”

All county and tribal health departments follow Centers for Disease Control and Prevention protocols for the investigations, which now include tracking close contacts that occured in the 48 hours before the onset of symptoms. Health departments also monitor patients and close contacts daily, and arrange grocery and pharmacy deliveries, if needed, to help them maintain quarantine. Gallatin County implemented a legally enforceable rule on April 15 that requires people who’ve tested positive and close contacts identified by the health department to stay home.

Urban counties had resources to retrain staff or hire new people. As in Gallatin, the health departments in Missoula and Yellowstone counties ramped up by bringing on additional staff,  14 in the case of Missoula and 11 for RiverStone Health in Yellowstone.

Even so, it’s a challenge. “It is stressful, and it’s a lot of information to process,” Gallatin County’s Spinelli said. “If you don’t have a couple of people you can lean on and they can lean on you, I think that would be a lonely hard job right now.”

Toole County, the center of the largest rural outbreak in the state, had less funding and fewer qualified people to draw on. There, the virus infected 20 people associated with the Marias Heritage Center, a long-term care facility in Shelby. To contain the outbreak, two people in the health department have been working seven days a week and 10-plus hours a day, according to an email from the department. Because three of the close contacts lived in neighboring counties, the Toole department worked with the state to pass off contacting and monitoring those potential patients to their home county health departments.

Toole and Gallatin counties also offer another point of contrast.

“At what point can you not keep up with it anymore, because you don’t have the workforce capacity, or it gets too crazy to keep track of?”

—Lake County Public Health Director Emily Colomeda

“In the case of Toole County, it was a much smaller group of individuals that were involved,” Murphy said. “That allowed for major identification of the people that needed to be quarantined and observed [and] it was easier to spot cases earlier. When you get into an area where you have a lot of cases, like Gallatin, some of the cases don’t know where they picked up the infection. … That changes the dynamic a lot, because there are cases they can’t associate easily with another case, meaning community spread is occurring, and that makes it more challenging to stay on top of it.”

Elsewhere in Montana, public health workers are also working overtime. In Carbon County, which has six confirmed cases as of April 17, the two public health nurses take turns being on call overnight. They phone every close contact immediately after receiving a positive test result, keeping everyone anonymous as they move down the list. With interviews and documentation, an investigation involving five contacts might take about three hours, according to Carbon County public health nurse Roberta Cady. But with Carbon County’s older population, the calls sometimes take longer.

“It can be a hard concept for them to grasp, and there’s a lot of education and explaining to each individual how this is all going to work,” Cady said. “Some people have a lot of stories to tell you, and they will go into the weeds about going to the vet or wherever they went. … You have to let them verbalize all that, and try to bring them around to the important questions.”

The primary work comes with the initial contact with the exposed person, Cady added.

“The time you spend with that person developing a rapport, the easier your phone calls will be for the next 14 days, because they’ll feel like they kind of know you. … If I wasn’t a nurse and somebody called me and said, ‘You’ve been named as a contact to a positive coronavirus [test],’ my first thing would be, ‘That’s wrong, or who? Or, who told you?’ Then, next, I’d be scared. … and then you start to accept it, and you realize you can get through it.”

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As useful as it is, contact tracing doesn’t catch every case of the virus. As Murphy said, “It’s only as good as the interviewer, and the [recollection of the] person being interviewed … of the places they’ve been where they would have actually made a difference with respect to risk.”

And then there’s the issue of asymptomatic transmission. With new researchshowing that up to 50% percent of infected people may not show any symptoms— and only people with symptoms getting tested — theoretically half of the origination points for spread could be going unnoticed. But Murphy says the math isn’t necessarily that simple.

“Think about somebody that’s symptomatic that’s coughing. … They’re spewing that virus out to [their] close contacts. If I’m asymptomatic, I might be high risk for my household contacts, because I might be carrying utensils, drinking from the same cups, or kissing my daughter goodnight. … But if I had to pick between a person that is asymptomatic and a person that is symptomatic, who would you rather sit next to?”

Another limitation of contact tracing is that its cost-to-benefit ratio can plummet as infections become widespread.

“Testing everybody would provide you a snapshot at one bit of time. … We’d have to test people literally every three days to have that be a viable strategy. Nobody’s really promoting anything like that.”

—Jim Murphy, chief of Montana’s Communicable Disease and Prevention Bureau

“At what point can you not keep up with it anymore, because you don’t have the workforce capacity, or it gets too crazy to keep track of?” said Lake County Public Health Director Emily Colomeda. As of April 17, Colomeda’s department, which works closely with the Confederated Salish and Kootenai tribes’ health department, had seen only four local cases, but Colomeda said the department will need help if infections go up.

If an outbreak becomes so widespread that contact tracing can’t keep pace, public health workers sometimes prioritize tracking and testing for the highest-risk populations, like the elderly or immunocompromised.

“There are limits to contact tracing, and you have to make some tough decisions sometimes,” Murphy said.

On April 10, NPR reported that the CDC is working on a plan to scale up testing and implement “very agressive” contact tracing, according to agency director Robert Redfield.

“We are going to need a substantial expansion of public health field workers, and it is going to be critical,” Redfield told NPR.

Redfield said the CDC has more than 600 field workers already, and plans to “substantially amplify that.” He didn’t say when or how the agency will ramp up, only that it would be soon.

“Obviously, if we’re going to try to get this nation back to work shortly after the end of this month, we’re far along in those planning processes as we speak,” he said, referring to President Donald Trump’s announcement that he wants to begin re-opening the economy by May 1.

It’s unknown whether Montana would receive new field workers to help expand contact tracing efforts. “We wouldn’t rule out that kind of help,” Murphy said, “but right now, [with] what we have, the local health departments are managing quite well.”

Redfield said the CDC is also evaluating the potential of using technology to make contact tracing “more efficient and effective.”

East Asian countries including China and South Korea have implemented various tracking systems via cell phone and credit card data to monitor infected persons’ whereabouts, some of which have been applied by government mandate. Several local governments in the U.S. are about to launch a tracing app that uses Bluetooth to anonymously share the location of people who’ve tested positive with the phones of others who were close enough to be exposed. A similar app is in the works in Europe, and Apple and Google this week jointly launched an app that tracks a COVID-positive person’s location, theoretically without privacy risks.

While the technology has promise, Murphy said, it won’t be a perfect fix.

“First of all, not everybody’s using [the apps]. Second, just the fact that you crossed paths with someone doesn’t make you a close contact with them — it might for measles, but it doesn’t necessarily for COVID. … Right now there’s not a good replacement for a good, diligent public health nurse that can do a good interview with somebody who they caught in time. It’s hard to replace that with an app.”