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What is contact tracing, and how does it work?

September 08, 2020

Imagine you wake up one morning with a cough and a fever. You think to yourself: “Could it be coronavirus? How could I have been exposed?” You call your doctor, and they order a test. Perhaps you’ve been doing all the right things, but you still get the dreaded result: positive for COVID-19.

Thinking back to the 2–14 days before your symptoms came on (COVID’s typical incubation period), you start a mental checklist: You went to the grocery store, you talked with a friend from six feet apart (or was it closer than that?), you helped a neighbor move a couch. Could any of these interactions have caused your infection? And during that time, who could you have infected?

This thought process, and the knowledge that outbreaks like coronavirus spread exponentially, is the basic idea behind contact tracing.

Limiting the spread of infection

While there are many high-tech approaches to contact tracing, in its most basic form tracing simply means identifying who a sick person has interacted with recently to figure out who they might have exposed. Those exposed people must then isolate themselves to limit further spread.

In other words, limiting the spread of a disease means stopping some infections before they start.

According to Johns Hopkins Medicine, which offers resources and guidance for tracing the spread of COVID-19, the overall goal of contact tracing is to:

  • Break the chain of transmission in contagious disease outbreaks
  • Prevent local surges in the number of sick people that can overwhelm hospitals and resources
  • Hasten the ability of communities to safely reopen schools, businesses and public areas

As the New York Times reports, some countries have been highly successful at containing the virus this way:

“Contact tracing has helped Asian countries like South Korea and Singapore contain the spread of the virus, but their systems rely on digital surveillance, using patients’ digital footprints to alert potential contacts, an intrusion that many Americans would not accept.”

How does contact tracing work?

The alternative to the more intrusive digital tracing is people. Back in April, Massachusetts hired around 1,000 people for an ambitious program called the Community Tracing Collaborative, which has since become a model for the rest of the country. The program’s contact tracers do the work of reaching out to people who have been exposed to the coronavirus.

According to, “The program focuses on reaching out to people who have tested positive for COVID-19 and the contacts they have been close to, making sure they have the support they need to isolate or quarantine. When the MA COVID Team calls, you can do your part by answering the phone and providing helpful information that will help flatten and reduce the curve in Massachusetts.”

How is contact tracing conducted for COVID-19?

When someone tests positive for COVID-19, the contact tracer follows these steps:

  1. Contact the infected person and encourage them to isolate before others can be infected.
  2. Work with that person (confidentially) to figure out who they may have been in contact with while they were contagious.
  3. Contact people who may have been exposed and inform them of the risks and symptoms of COVID-19 and encourage them to self-quarantine.

What are the downsides of manual contact tracing?

Tracing contacts through human means is imperfect because success relies on each subject’s memory. It can also be slow, making subsequent exposure difficult to prevent.

Slowness is usually caused when tracers have trouble getting through to contacts. Many people don’t answer the phone for unfamiliar numbers – so one thing you can do to help is pick up the phone, just in case.

Still, while human outreach is flawed, it is considered a standard and effective public health measure.

Notably, it was important in stopping the 2014 Ebola outbreak.

To stop the spread of Ebola, the Centers for Disease Control and Prevention asked sick people to provide lists of their recent interactions with family, friends, and businesses. The contacts on that list would then be monitored for illness for several weeks.

In Massachusetts, Governor Charlie Baker says he will stick with human contact tracing as a tried and true method:

“You’ve got to be able to connect to people in some way that’s meaningful that’s beyond a ping on the phone,” he told the New York Times.

What is the role of contact tracing in reopening plans?

Infectious disease experts have recommended certain key measures we can all take individually to fight the pandemic:

  • Social distancing
  • Mask wearing
  • Staying home when sick
  • Handwashing

Across the country, states have worked to put strategies in place to guide the reopening process.

The Massachusetts reopening plan identifies the following measures as keys to opening safely:


Increase testing capacity and number of people tested so people with COVID-19 are aware of their diagnosis and can self-isolate.

Contact Tracing

Trace all contacts of people with COVID-19 to ensure safe quarantine and testing for those who need it.


Minimize transmission by isolating and quarantining individuals with COVID-19 and their close contacts.


Provide support so individuals can safely isolate and quarantine.

What should you do if you were around someone with COVID-19?

If you are identified as having been in close contact with someone with COVID-19, you may get a call from the health department.

It is important to stay home and away from others, and to monitor your health for symptoms of COVID-19. Symptoms may appear 2-14 days after exposure. Many people who are infected with COVID-19 never show any symptoms but can still spread the virus. Therefore, it’s important to quarantine whether or not you develop symptoms.

According to the CDC:

“For COVID-19, a close contact is anyone who was within 6 feet of an infected person for at least 15 minutes. An infected person can spread COVID-19 starting from 48 hours (or 2 days) before the person had any symptoms or tested positive for COVID-19.”

Contact tracing for COVID-19 works best with other preventive actions

It is important to continue to slow the spread of COVID-19 by taking the recommended preventive actions.

If you have questions or concerns about COVID-19 or think you may have been exposed, talk to your healthcare provider or contact an urgent care center.