The lawsuit, filed in McHenry County, accuses the district of negligence, saying it knowingly allowed an employee with E. coli to handle food.
The families say the two students involved suffered permanent injuries after eating contaminated lettuce in September 2023.
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Sixteen people became ill, the lawsuit said.
The school said it can't comment on current litigation, but said in a statement "Throughout the process we were in full cooperation with the McHenry County Department of Health."