CHICAGO (CBS) — The wide number of people the president came in contact with this week expands the number of people who need to be contact traced to help stop the spread of COVID-19 following his positive test. University of Chicago doctors are calling this a watershed moment.

In the last 24 hours CBS 2 has learned about cases from the White House to Lane Tech College Prep High School in Chicago. Contact tracing is underway in both cases.

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The process dates back to the plague and was given its name during the Spanish flu.

“It’s definitely a milestone in this pandemic,” said Dr. Aniruddha Hazra of the University of Chicago.

Hazra compares COVID019 spread to a tree.

“You have this tree that is branching out branch by branch off the main trunk itself,” Hazra said.

The longer the branches, the strong the tree, and the hard it is to control the spread. Hazra said the best tool to fight it is “identifying and limiting contact with people with COVID-19. The virus stops spreading,” according to the Centers for Disease Control and Prevention.

Contact tracing is the process of reaching out to all people who came in contact with a patient in the days since infection and having them test and quarantine if positive.

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“What you’re doing is trying to stop that from growing any further,” said Hazra. “The president’s contact tracing is probably to a higher degree than what we are able to do in the community, just based on resources.”

A public not eager to share information from a cold caller and the lack of national tracing infrastructure are hurdles to better, deeper tracing, but the biggest hurdle is getting patients to remember 14 days of interaction.

“That can be challenging for folks to recall and submit that kind of information,” Hazra said.

As the White House works through the hundreds of people the president interacted with in recent days, parents at Lane Tech on Chicago’s North Side received a letter Friday morning notifying them of a student who contracted the novel coronavirus.

Upon learning the news, the school did a deep clean and notified parents. Buildings are back open in a limited capacity.

Doctors say it is too early to know whether these cases are a continuation of summer trends or a sign of a fall spike.

“The coronavirus doesn’t discriminate as to who is susceptible and who it potentially can affect,” Hazra said. “Part of me hopes it triggers some folks to potentially take it a little bit more seriously than they were before.”

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Contact tracing is regularly utilized in cases of HIV and AIDS. It was most recently used in large scale form during a measles outbreak at Disneyland six years ago.