CHICAGO (CBS) — There are worries about a large office building in the Chicago suburbs where a man visiting from out-of-state, had a fever and later was diagnosed with COVID-19 after he returned home.

CBS 2’s Mike Puccinelli reports from Glenview to explain how this curious case came to light.

That visitor is an employee of CVS in Massachusetts. He visited a Glenview location last week. CBS 2 learned of the case from a tip on Tuesday. That’s the same way Glenview authorities got notified.

The story begins with an email addressed to officials in the northern suburbs: “I am writing to let you know that you have a potential health crisis brewing in your backyard.”

The reason?

Someone infected by COVID-19 during an outbreak in Boston spent an entire day there. The email goes on to say that infected CVS employee met with his team and dozens of others. He was on multiple floors, in multiple conference rooms and rode multiple elevators.

That person then flew back to Boston with a fever and tested positive on Saturday. CVS said it learned of this on March 8, Sunday. The office was disinfected and those who worked close to the employee are quarantined.

The Glenview Northbrook coronavirus website claims no cases. CBS 2 found no one told Northbrook or Glenview officials. The deputy village manager of Glenview said it learned of this case from the same email CBS 2 received.

Now the Cook County Health Department is investigating. The Glenview official also reached out to CBS 2 for more information.

CVS officials were not available to go on camera. They said all of the areas of the building where the employee worked have been disinfected. It added that all non-essential travel is now banned company wide.