'Contact Tracing' Tracks People Who May Have Been Exposed to the Coronavirus—Here's How It Works

Will it help control outbreaks—and what are the privacy concerns? Experts lay it all out.

"Contact tracing" is a measure many states and nations around the world plan to use to curb the spread of coronavirus when lockdown restrictions are eased. The Centers for Disease Control and Prevention (CDC) described it on April 22 as “a key strategy for preventing further spread of COVID-19” and warned that “immediate action is needed.”

But what does contact tracing mean, and how does it work?

Here's how contact tracing works

Contact tracing starts with people who’ve been diagnosed with COVID-19. “Contact tracers are individuals who interview those people and determine who has potentially been exposed to them, and when,” infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health.

When a confirmed COVID-19 patient identifies a specific person who they interacted with recently, the contact tracer will notify and then monitor that individual. “If they develop symptoms, doctors can quickly intervene, which can limit the chain of transmission,” says Dr. Adalja.

What states are conducting contact tracing?

In the US, contact tracing will be carried out at a state level. Massachusetts and Minnesota have already started using contact tracing, according to ABC News. New York is launching a contact tracing program as well. An estimated 2,200 contact tracers are making the phone calls, according to a report by the Association of State and Territorial Health Officials (ASTHO). But that only works out as one contact tracer for every 150,000 Americans—not enough, says ASTHO.

For the safety of both contact tracers and the public, contact tracing occurs digitally as much as possible. “Virtual call centers are coordinated with contact tracers calling from a private space, which could be in their homes,” Anna Bershteyn, PhD, an assistant professor in the department of population health at NYU Langone Health, tells Health.

Experts say contact tracing must be part of a second attempt to stop the spread of the coronavirus. “The early spread of the coronavirus wasn't stopped because testing was limited and the epidemic grew so rapidly,” says Bershteyn. “As social distancing decreases the number of COVID-19 infections, we will get over the peak of the epidemic and can take another shot at containment.”

The practice and scope of contact tracing varies. In Ireland, tracers are making more than 5,000 calls a day to people who have been in contact with confirmed coronavirus cases. According to The Irish Times, friends, family, neighbors, and others who interacted with every confirmed COVID-19 patient have been contacted, which involved calling around 40 people per person.

Germany and South Korea started contact tracing weeks ago; France, Belgium, and the UK have announced plans to begin the process.

How did contact tracing originate—and how well does it work?

Contact tracing is not a new thing—although most of us hadn’t heard of it until the age of COVID-19. “Contact tracing is used in many different outbreaks, ranging from measles to Ebola, throughout the world,” says Dr. Adalja. “It is routinely done in the US for both measles and tuberculosis. Sexually transmitted infections also are sometimes contact traced.”

While contact tracing can be highly successful if health departments have the resources they need to perform the task, it comes with limitations. For starters, not everybody can remember who they’ve been in contact with, besides family, friends, and colleagues. And some types of transmission can be missed.

“The virus can transmit through high-touch surfaces such as door handles and elevator buttons, when people who touch them forget to wash their hands before touching their eyes, nose, and mouth,” says Bershteyn. “Those transmissions are difficult to trace. So even with contact tracing, we must be on the lookout for new outbreaks in the general population.”

Difficulties of tracing an infected person's contacts

Bershteyn says it can also be challenging to get everyone diagnosed with COVID-19 to agree to contact tracing because of privacy concerns—as well as possible skepticism around whether being traced is in a person's best interest. “That’s why contact tracing is often bundled with helpful resources, like useful information, supplies to safely care for sick people at home, and connections to health care and other necessities,” she explains. “It's also important to establish trust and to communicate clear policies around what will happen if someone is identified through contact tracing, so people are not afraid of what might happen to them.”

It’s no surprise that contact tracing can be more successful when there is a small number of contacts versus a mass exposure, such as at a concert or festival. Bershteyn adds that it’s most useful when the total number of confirmed cases in a given geographical area is low.

“That’s the point where we can switch from general mitigation to more targeted containment efforts,” she says. “Different communities will reach that point at different times, depending on how rapidly their epidemics decline. The timing will depend on a number of factors, including when the epidemic began in a community, and how rapidly and strongly the community responded to the epidemic.”

The role of technology in contact tracing

One possible way to make contact tracing more successful on a large scale is by tapping into technology. Software developers around the world have been working on contact tracing smartphone apps, which alert users when someone they were recently near becomes infected with the coronavirus. Some places are using another technology—wireless Bluetooth signals—to identify contact matches. According to the CDC, the “adoption and evaluation of digital tools may expand reach and efficacy of contact tracers.”

But even the people behind the technology have their doubts as to whether digital tracing could replace the old-fashioned manual sort. "If you ask me whether any Bluetooth contact-tracing system deployed or under development anywhere in the world is ready to replace manual contact tracing, I will say without qualification that the answer is no, not now and, even with the benefit of [artificial intelligence], not for the foreseeable future," Jason Bay, who led development of Singapore's TraceTogether contact tracing app, wrote on April 10 in Medium.

The CDC has recommended that “large cadres of contact tracers” be employed in all areas of the US. If you’re wondering whether you’re suitably qualified, Dr. Adalja says the role doesn’t require extensive training, but good interpersonal skills and organization are crucial.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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