CHICAGO (WLS) -- As Illinois moves into Phase 4 of reopening, an alarming COVID-19 surge is happening nationwide, and it's primarily affecting a different group of people.
"The overwhelming majority of people getting affected are young people, likely the people that are in the crowds enjoying themselves," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
RELATED: Illinois COVID-19 cases increase by 857, with 39 new deaths
In Chicago between June 17 and 24, over a quarter of new COVID-19 cases were people aged 18 through 29, the biggest increase for any age group. New CDC guidelines say people younger than 65 are at risk.
That does not come as a surprise to Northwestern Medicine's Dr. John Coleman.
"Our general ICU population has always been around 30 to 60, so the fact that they are acknowledging this is a change in the CDC guidelines, but young people have always been at risk," Coleman said.
Coleman has spent the last three months treating the sickest COVID-19 patients. He said underlying conditions like diabetes and obesity are not always contributing factors for younger cases.
"A lot of them don't have underlying conditions," he said. "They are young healthy people that got sick."
And even if they don't get sick, doctors say younger people can easily pass the virus on to someone else.
The new CDC guidelines also say pregnant women may be at an increased risk for severe illness compared to others in the same age group.
"We saw it with MERS, SARS and some strains of influenza, pregnant women due to the physiologic changes that happen in pregnancy, they are more susceptible to respiratory illness," said Dr. Emily Miller, OB-GYN with Northwestern Medicine.
Miller said if the mother is severely sick with COVID-19, her baby is at risk too. Fortunately, while cases are on the rise among younger people their death rates remain low.
While younger people and pregnant women are at risk, doctors say don't panic; they are still far from the majority of people who can get very sick from COVID-19.
Chicago coronavirus cases in young people grow noticeably in recent weeks
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