One Prudential Plaza owner Sterling Bay said in statement today the employee has been isolated and has not returned to the building since the diagnosis. Building tenants have been advised to stay home if they feel ill and to contact a health professional if they experience symptoms.

The person who tested positive is an employee of CA Ventures, the real estate developer told Crain’s, noting that the employee has not been at its Chicago headquarters at One Prudential Plaza since March 3.

"Individuals whose work areas are in close proximity to the affected individual have been notified and, although none have presented symptoms, they will remain under self-quarantine for the next 14 days," a CA Ventures spokesman said in an email.

The spokesman said the company is taking “every precautionary measure possible,” including asking staff to work remotely while the Chicago office is sanitized in accordance with CDC guidelines. It has also suspended all non-essential staff travel and meetings.

The building, 130 E. Randolph St., will stay open, but tenants are encouraged to discuss the logistics of work-from-home programs if they feel it’s necessary, according to a letter tenants were sent yesterday from the building.

Tribune Publishing is Prudential Plaza's biggest tenant. "We are exercising extreme caution by encouraging Prudential-based employees to work from home in response to a confirmed case of coronavirus at Prudential Plaza," Max Reinsdorf, a spokesman for the company, said in a statement.

"We will continue to follow all cleaning and disinfection recommendations put forth by the Centers for Disease Control & Prevention and World Health Organization and have been aggressively cleaning all high-touch areas throughout the building,” the letter to tenants says.

Michael Cornicelli, executive vice president at the Building Owners & Managers Association of Chicago, said he is unaware of any other Chicago office building where a person who has tested positive for the coronavirus works.