To Tell or Not to Tell

You sit in the office for the rest of the day, even eating lunch there. Towards the end of the day, students start coming in not feeling well. All of the sudden the phone is ringing off the hook, and teachers are running though the hallways shouting, "Kids are throwing up!" and "They are passing out on the floor!"

Fire trucks, police cars, and ambulances are surrounding the school when they evacuate the un-sick students. How did they get sick?