Not sure if it’s applicable to IL but here in MN if you have flu-like symptoms and test negative, you are still not supposed to show up for or return to class until the greater of either 10 days or three days following the disappearance of symptoms has passed. My high schooler’s principal is currently quarantined at home even though she tested negative. She wasn’t allowed to enter her (public) school building (nor was she attempting to - she was sharing with us what level of health protection measures were in place). During a normal year, it’s pretty common to have the same bug just rip through a house or dorm. This year might be different, of course, as the protocols will protect against more than just coronavirus infection. But in any event, if IL has a similar health order, then it’s possible that students catching something else will still end up quarantined and doing remote learning until their symptoms pass.