Delta variant continues quick spread across Illinois

  • Only about 10% of the state's positive COVID-19 tests are sent to labs for genomic sequencing to determine what strain of the virus caused the infection.

    Only about 10% of the state's positive COVID-19 tests are sent to labs for genomic sequencing to determine what strain of the virus caused the infection. Associated Press/March 4

Updated 7/25/2021 9:15 AM

During the past week, 279 new variant cases of COVID-19 have been diagnosed in Illinois.w

Illinois Department of Public Health researchers said Friday that 72% of the new variant cases -- 200 in all -- were the highly contagious delta variant.


While that may seem like a small number, keep in mind only 10% of the state's positive test samples are sent to labs each week to have genomic sequencing performed to identify the proliferation of variants, health officials said.

"We are now seeing delta replacing what has been the most common strain," IDPH spokeswoman Melaney Arnold said. "Alpha was replaced by gamma, and now the rate of growth with delta indicates that it will replace gamma."

And it's growing quickly. Since the start of this month alone, cases of the delta variant have more than quadrupled, according to IDPH records. The gamma variant caseload has grown by 4.5% during the same period.

The delta variant is single-handedly causing the spike in cases seen not only in Illinois during the past month but also in the nation. It is the strain of COVID-19 that was responsible for an incredibly deadly COVID-19 outbreak recently in India.

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"As the delta variant becomes more prevalent nationally, we are seeing that it spreads more easily than other variants," said Dr. Sana Ahmed, a medical epidemiologist at the Lake County Health Department.

According to U.S. Centers for Disease Control and Prevention figures, nearly 80% of all new cases diagnosed between July 4 and July 17 in the Great Lakes region -- Illinois, Indiana, Minnesota, Michigan, Ohio and Wisconsin -- were delta variants. That rate is higher in some bordering states, CDC figures show.

Missouri's infection rate has exploded in the last month, and many Illinois counties along that border are now seeing a massive spike in cases that most officials believe will turn out to be delta variants. The CDC estimates 96% of all new cases in Missouri, Iowa, Kansas and Nebraska are delta variants.

"Predominantly, the patients we're seeing with severe infections are unvaccinated, and unfortunately many of them have made poor choices first off not to get vaccinated, then they travel to hot spots like Florida, Oklahoma and Missouri," said Dr. Jonathan Pinsky, medical director of infection control and prevention at Edward Hospital in Naperville.


Dr. Rachel Rubin, co-lead attending physician at the Cook County Department of Public Health, said cases are rising because the delta variant is highly transmissible and more contagious.

"We're certainly seeing a rise in cases within our jurisdiction," Rubin said. "That's why we're urging everyone to follow CDC guidelines and wear a mask indoors if you're not vaccinated."

IDPH updates the variant case information every Monday, Wednesday and Friday on its website,

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