ASK QUESTIONS. Fever of unknown origin or FUO tends to be extremely frustrating and at times frightening. The workup for this problem tends is extensive, long and unfortunately expensive. The reasons for this is that FUO can be caused by so many different problems and on rare occassions may go away before a daignosis is made. You must stay on top of the mds following your daughter and asking what tests are done.
Fever unknown origin. The cause of FUO varies with age. Infection, usually atypical (or otherwise they would have figured it out), is always a possibility--consider tb, brucella, salmonella, malaria, hiv, etc. Cancer or leukemia is a possibility. Rheumatologic or autoimmune diseases (like lupus, rheumatoid arthritis, etc.) too. Drug reaction. 12% have no cause identified, and these cases have good outcomes.