The P.1 variant was first identified in the U.S. at the end of January, and has been identified in several states since then.
Health officials say the case in Chicago was identified by the Pathogen Genomics research team at Northwestern University Feinberg School of Medicine through sequencing analysis of a COVID-19 specimen.
CDPH then investigated and found that a household contact of this individual also had COVID-19. However, neither individual nor any person in their household reported travel outside of Illinois.
Officials say the P.1 variant can spread more easily than other circulating strains of COVID-19.
There is also some evidence that the variant may affect the ability of antibodies to recognize and neutralize the virus. However, researchers say more studies need to be done.
Health officials still encourage the same strategies to contain the spread of COVID-19, including wearing a well-fitting mask; practicing social distancing; avoiding gatherings; limiting travel; and washing your hands often.
The Sun-Times contributed to this report.