A fever that has not cleared up for a long time is usually caused by the cause of the illness not being completely eliminated. Fever can be caused by bacterial or viral infections, as well as other illnesses. Fever caused by bacterial or viral infection is very common. If you just take fever-reducing medication without treating the original disease, the fever will persist or recur. If the fever is caused by a bacterial infection, it can be treated with antibiotics, such as penicillin and cephalosporins. If it is caused by a viral infection, ribavirin can be used in certain cases, and oseltamivir can be taken if it is an epidemic virus. Having other illnesses can also cause a persistent high fever, such as leukemia or severe neoplastic disease, which also requires treatment of the primary illness. If the fever persists or recurs, you need to go to the hospital as soon as possible to clarify the cause, and the doctor will formulate an individualized diagnosis and treatment plan according to the specific condition, so as to avoid delaying the condition.