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Coronavirus contact tracing: Why experts say it could pave the way to normalcy

Old school epidemiology meets mobile data, but not without a price.

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Before we can defeat the coronavirus, we have to know who might have come into contact with it. To do that, a growing number of scientists and governments have argued that a combination of old-school epidemiology and mobile data could be the solution.

Those concepts united are known as "contact tracing" — and some experts say that the time to use contact tracing in the fight against Covid-19 is now.

In line with that, on Thursday April 2, Google announced it would publish reports of community mobility data, showing just how much travel patterns have changed since quarantines have gone into effect.

Google isn't the first that we use location data, but this project is certainly one of most high-profile efforts to use such data so far. The firm will utilize data from those who have opted to share their location history to indicate where stay-at-home orders are being respected. (Check out your county here.)

Before Google's announcement, efforts to create similar projects were already underway,

On Wednesday, scientist Trevor Bedford, a virologist at the University of Washington, tweeted about the launch of a contact tracing project called NextTrace, which would help alert people if they had been exposed coronavirus cases.

Another initiative called Pan-European Privacy-Preserving Proximity Tracing (a soon-to-be-incorporated Swiss non-profit) also announced a similar project the same day — and gained the endorsement of German Chancellor Angela Merkel, who is currently in quarantine.

"I would of course also be prepared to use it myself to help other people," she said of the app.

These are high-profile efforts that require technical expertise, but they're based in old-school epidemiology.

What is contact tracing? — Contact tracing is a basic form of epidemiology used to contain infectious diseases. It's a process that scientists use to figure out who a patient — who has tested positive for a certain disease — may have been in contact with. They do this by interviewing the patient or making phone calls.

It's basically like having a doctor retrace your steps, but instead of trying to find your lost keys, they're trying to figure out where you may have left behind the coronavirus for someone else to encounter.

We already know that contact tracing works: A 2006 study found it particularly useful for the containment of SARS. But it's typically done during the early stages of an outbreak when prevalence is not extremely high. As cases skyrocket, the legwork required to trace someone's contacts becomes hard and harder to do.

A graphic explaining how digital contact tracing would work.


This is especially the case when it comes to the coronavirus, where the disease is widespread. It's compounded by the fact that some cases occur in patients who don't feel sick, but are spreading the virus anyway. (Robert Redfield, the director of the Centers for Disease Control estimated that about 25 percent of cases are transmitted this way.)

Enter digital contact tracing: That's the idea that we could use a combination of mobile location data and self-reporting to alert people if they've been exposed to Covid-19. In such a system, once someone tests positive, everyone who was nearby (found using location data or Bluetooth information) receives a notification letting them know they're been exposed.

Who is already using digital contact tracing? — In a paper published Tuesday in Science, a team argues that digital contact tracing would reduce the R0 of the coronavirus (a measure of how many people are likely to be infected by each person with the disease) to less than one. That's enough to contain the spread, the authors report.

"Digital contact tracing could play a critical role in avoiding or leaving lockdown," they write.

China currently has a form of digital contact tracing built into two popular apps: Alipay, an all-encompassing shopping app, and WeChat.

The app already uses location data and "government background system information" to assign "color" codes (green, yellow, red) that correspond to coronavirus exposure. Those color codes dictate whether someone is allowed to leave self-quarantine, and participate in public life.

There are clear privacy concerns with such an app. The Chinese system shares location data and disease status with law enforcement agencies, according to a New York Times investigation.

What is "participatory digital contact tracing?" — Bedford's proposed version of digital contact tracing works differently. Their effort is technically called "participatory digital contact tracing" which is an important distinction, privacy-wise. The data is also anonymized.

In the case of NextTrace, someone would choose to have their positive, confirmed case status uploaded in an app. Then, the app would use location data to alert people who had been nearby that they may have been exposed to a case — if they opt-in.

Still, while if this differs from China's approach, there's been criticism that such an app can increase stigma towards those who test positive.

For example: South Korea's version of digital contact tracing released detailed information that could lead to that issue, as Anne Liu, a global health systems expert at Columbia, explained to Science.

"They’re essentially texting people, saying, ‘Hey, there’s been a 60-year-old woman who’s positive for COVID. Click this for more information about her path,'" she said.

Ultimately, the purpose of digital contact tracing is to be able to make social distancing policies less "blunt" and more targeted at people who have either been exposed to the virus directly or actually have it.

But knowing who actually has the virus also requires widespread coronavirus testing, something that the United States has struggled with. Digital contact tracing still has hurdles in terms of privacy, equitability and testing to overcome, but it could soon become a bigger part of the anti-coronavirus battle plan.

Editor's note 4/3/20 10:53 a.m.: This story has been updated to include mention of Google's new project.

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