Elizabeth Steinberg was a healthy 16-year-old student on the tennis team at St. charles high school, west of chicago, illinois. But then she started to have strange health problems. The same thing happened to dozens of teachers and student at the school. They went to doctors for treatment of a number of symptoms such as sore throats, tiredness, headaches, and respiratory (breathing ) difficulties. Doctors treated respiratory infections with antibiotics, but the condition didn’t seem to improve, except-mysteriously-on weekends and over vacations, when the symptoms disappearesly.