Illinois Dept. of Public Health changes definition of school outbreak from two connected cases to at least three

The move comes after the Centers for Disease Control and Prevention updated its guidance

The Illinois Department of Public Health now considers a school outbreak as “multiple cases comprising at least 10% of students, teachers or staff within a core group or at least three cases within a specified core group. A core group means only those individuals who were together during an exposure period.”

According to a news release from the state of Illinois, the move comes after recommendations from the Centers for Disease Control and Prevention to adopt the Council of State and Territorial Epidemiologists’ guidance for pre-K to 12 school-associated outbreaks. Previously, the CDC recommended that two cases associated with a school would constitute an outbreak.

For example, now an outbreak 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.

“In an effort to more confidently establish whether transmission of COVID-19 occurred in school versus another location, [the] IDPH is following [the] CDC’s recommendations and adopting Council of State and Territorial Epidemiologists’ guidance, which updates what is considered to be a school-associated outbreak,” IDPH Director Dr. Ngozi Ezike said in the release. “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.”

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, according to the release. 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 also must be epidemiologically linked to the school setting or extracurricular activity, meaning they were at the same place at the same time.

More information about school outbreaks, exclusion and guidance 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, at