Adults with a fever of 39 degrees may be caused by bacterial infection, viral infection or rheumatoid arthritis, etc. You can combine the cause of the disease by physical cooling, oral medication and other methods to reduce fever. 1. Bacterial infections: If a bacterial infection causes a fever of 39 degrees in adults, you need to use acetaminophen, amoxicillin, cephradine capsules and other drugs under the guidance of a doctor to treat the physical condition. If the symptoms are more serious, you need to change the oral medication to intravenous infusion. At the same time also need to drink more water, to avoid the body temperature continues to rise, the phenomenon of electrolyte disorders. 2. Viral infection: If the adult fever of 39 degrees caused by viral infection, you can first take physical cooling, such as taking a warm bath or using warm water to wipe the body, can make the body temperature down to a relatively calm state, can avoid the body temperature drop too fast, resulting in the body’s immune response to decline. If the symptoms are severe, antiviral and antipyretic medications can be used, such as oseltamivir and acetaminophen. 3. Rheumatoid arthritis: If rheumatoid arthritis causes a fever of 39 degrees in adults, you can first use non-steroidal anti-inflammatory drugs under the guidance of a doctor, such as diclofenac sodium, ibuprofen, and celecoxib and so on. If necessary, a combination of low-dose glucocorticosteroids, such as prednisone acetate, can also be used. Methotrexate is also used to control the progression of rheumatic disease. If the disease continues to be unrelieved by the above methods, it is necessary to go to the hospital for medical treatment.