Doctors have continued to test Jason Overman, a 6-year-old cancer patient from Orem, but they can't find the source of the fever he developed Monday.

"They have tested for a lot of serious diseases, and we are happy to at least know what it's not," Lorraine Hill, Jason's aunt, said Thursday. "The doctors don't think it's anything serious, but they want to hold Jason for observation."Jason has been a patient at UCLA Medical Center since a bone-marrow transplant Aug. 18. He suffers from neuroblastoma, a rare childhood cancer that attacks the nervous system.

After Jason's condition was diagnosed in February, Utahns helped raise money for the transplant - Jason's best hope of surviving his cancer. Friends, neighbors and strangers organized auctions, petting zoos, dunking booths, performances, dances and bake sales. They collected $192,000 for Jason's hospital bills.

Doctors had announced last week that Jason was doing better than the average marrow-transplant patient and there was an 80 percent chance he could be released Friday to Primary Children's Medical Center in Salt Lake City. The fever Jason got Monday canceled his travel plans, but when it dropped slightly, his family had hoped he could make the trip early next week.

"We are at least happy Jason's fever is not as high as it was," Hill said. "But the doctors say Jason will stay at UCLA until they know something. They have done a lot of tests, but haven't confirmed anything yet."

Two weeks ago, Jason had a serious bout with graph-vs.-host disease, Hill said. About half of all marrow-transplant patients suffer some degree of the disease, said Vicki Beck, UCLA Medical Center spokeswoman. The disease occurs when donated marrow rejects its new body and attacks it.

Jason receives platelets, removed from donated blood, to help his blood clot. He also receives blood transfusions and antibiotics - normal treatment for a transplant patient. He is fed intravenously.

Hill said Jason will not be able to live at home until he is well enough to not need the transfusions and to eat solid food. She said it could take up to a year for his white count to return to normal. White blood cells help the body fight infection. Jason's white blood cells were destroyed by chemotherapy and radiation used to treat his cancer.

Hill said radiation treatments have made Jason's mouth and throat so sore that nurses must use soft sponges to clean his teeth and gums.