Health officials said the case was found in a person who is fully vaccinated and has received a booster dose. They have not required hospitalization and their health is improving, the Illinois Department of Public Health said.
The patient had contact with an out-of-state visitor who tested positive for the omicron variant, and is self-isolating as they recover, officials said.
Folks, the state’s first #Omicron case has been confirmed in Chicago. The resident—who was fully vaccinated with a booster dose—did not require hospitalization. They self-isolated when their symptoms began, and are improving. 🧵— Mayor Lori E. Lightfoot (@chicagosmayor) December 7, 2021
"We assumed that it was here, and now we've demonstrated that we can detect it," said Prof. Stefan Green, Regional Innovative Public Health Laboratory at Rush University. "And now it's really kind of just a waiting game."
More cases are likely to follow, including among those who have had contact with known omicron cases.
It's behind the scenes lab testing that detects variants. Arwady said so far 99.9% of positive COVID cases in Chicago are still the delta variant.
"It's kind of like a race between delta and omicron now," Green said.
If omicron overtakes delta as the dominant variant, scientists at the University of Illinois at Chicago could be among the first to know. Their analysis of wastewater samples in 40 Illinois counties has provided context on how the virus is evolving.
"In a lot of places we see trends in upticks before we see the trends in clinical case data," said Prof. Rachel Poretsky, UIC Biological Sciences.
The city's effort to address omicron, as well as all other variants of the virus, is focused on testing and vaccination.
The 11th floor of City Hall served as a Chicago Department of Public Health vaccination pop up site Tuesday as the city continues to push everyone to get vaccinated and boosted. CDPH Commissioner Dr. Allison Arwady expects Chicago's first omicron cases to be detected within the day as behind the scenes genome testing continues.
"We are following multiple individuals who we know had exposures, whether they were traveling in the US or internationally," she said.
As the country begins to grapple with omicron, the Centers for Disease Control has changed its guidance on home test kits, now urging anyone, even vaccinated people without symptoms, to use the rapid home tests before any indoor gatherings.
After Thanksgiving, CVS and Walgreens have seen a big uptick in the sale of home test kits. They run about $23.00 a box, but the Biden Administration has stated a goal to provide them to everyone for free. Until that happens, the city of Chicago plans to increase the availability of free home kits.
Whether it's a home rapid test or PCR, Dr. Arwady said neither is able to detect what variant you may have.
"When you get a test, whether it's an antigen test or a PCR test, the answer it gives you is yes/no; I have COVID or do not," she explained.
The World Health organization said early data shows omicron may be more transmissible than delta, but may not cause more severe illness. Health officials say more data is still needed to be sure.