CO Not Responsible For Sending Students To HospitalThe illness that made 30 Springfield Public school students sick enough to go to the hospital Thursday was not caused by carbon monoxide, according to the Minnesota Department of Health. A group of fourth and fifth graders became sick while rehearsing for a choir concert. On Friday, school officials say all the students are fine, and health officials think the illness may have been caused by nerves. Bethany Mattson says she was never really worried about her fifth-grade daughter, who was rehearsing with her classmates Thursday morning in the school's auditorium. But she can see why other parents may have felt differently.