An infant less than one year old died in Chicago, Illinois after testing positive for the novel coronavirus, the state health department said on Saturday.

Details: The death would mark the first reported infant mortality from COVID-19 in the U.S. The fatality rate for the novel coronavirus in the U.S. is highest among those over 85 years old, per the CDC.

What they're saying: "There has never before been a death associated with COVID-19 in an infant. A full investigation is underway to determine the cause of death,” Illinois Department of Public Health Director Ngozi Ezike said Saturday in a press release.

"We must do everything we can to prevent the spread of this deadly virus. If not to protect ourselves, but to protect those around us."

— IDPH Director Ngozi Ezike

The big picture: Most recorded cases in Illinois are currently in Chicago and the surrounding counties. The state health department has reported 3,491 COVID-19 cases as of Saturday, including 47 deaths.

The state recorded five deaths last Friday.

Flashback: The Los Angeles County health department in California said Tuesday "there may be an alternate explanation" for the death of a teenager whose "early tests indicated a positive result for COVID-19."

Go deeper: Illinois issues stay-at-home order amid coronavirus outbreak