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Illinois adopts CDC recommendations for school outbreak definition

The Illinois Department of Public Health (IDPH) is following recommendations from the Centers for Disease Control and Prevention (CDC) to adopt the Council of State and Territorial Epidemiologists (CSTE) guidance for PreK-12 school-associated outbreaks.

Previously, CDC recommended that two cases associated with a school would constitute an outbreak.

The new national recommendation that Illinois is adopting defines a school outbreak as either (1) multiple cases comprising at least 10% of students, teachers or staff within a core group or (2) at least three cases within a specified core group.


A core group means only those individuals who were together during an exposure period. For example, this could be limited to a classroom, a sports team, before/after school care, performing arts or other groups and likely does not apply to the entire school population.

More information about school outbreaks, exclusion, guidance, and frequently asked questions can be found on the IDPH website on a new COVID-19 Youth and School Resources page, including youth vaccination rates by county, youth cases over time, and youth emergency department visits.

“This change in criteria will continue to identify outbreaks and help prevent further spread, but also help rule out outbreaks that are not associated with the school,” said IDPH Director Dr. Ngozi Ezike.

To be considered part of an outbreak in a school, cases must meet the criteria for a probable or confirmed school-associated case with a positive test result, or the start of symptoms within 14 days of each other. These individuals are identified to be close contacts with each other while in the school setting and not another setting outside of school. The cases must also be epidemiologically linked to the school setting or extracurricular activity, meaning they were at the same place at the same time.

Masks are still required to be worn in schools by students, staff and visitors to help protect the health of those in schools and prevent further transmission in the community among vulnerable populations.

More information about the importance of using layered prevention strategies, including universal masking, to stop the spread and minimize disruptions to school operations for safe in-person education can be found in three new studies. These studies found that school districts without a universal masking policy in place were more likely to have COVID-19 outbreaks.

Nationwide, counties without masking requirements saw the number of pediatric COVID-19 cases increase nearly twice as quickly during this same period. Masking also helps keep students in school. In Illinois, a student who was within 3-6 feet of a case in a classroom setting is not considered a close contact if both the case and close contact were consistently masked for the entire exposure period.

IDPH recommends vaccination for individuals 12 years and older, including students. School personnel are required to be fully vaccinated or tested at least weekly for COVID-19, per Executive Order.

IDPH has also teamed up with SHIELD Illinois to provide free COVID-19 testing to all K-12 public schools across Illinois outside of Chicago.

As an alternative to exclusion from school, unvaccinated students and staff who have been identified as a close contact of a positive COVID-19 case now have the option of a Test-to-Stay protocol, as long as both the case and contact were masked during the exposure. Close contacts must be tested on days 1, 3, 5, and 7 after exposure. As long as close contacts remain negative, they are allowed to remain in school.

Participation in weekly screening testing at school is strongly encouraged as an added layered mitigation strategy and to support implementation of Test-to-Stay.

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