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Chronic fever, often also called fever of unknown origin (FUO), is a fever that keeps recurring or doesn’t relent and doesn’t have an immediate explainable cause, like an obvious viral or bacterial infection. Such a condition may have numerous causes, and doctors advise people not to ignore this symptom. The degree to which FUO is serious depends on its source, but since it may suggest serious illness, a doctor’s visit is warranted.
Many times doctors look first to one of the obvious causes of continuous fever: infection in the body. This could be relatively hidden and might be due to an abscess somewhere in the body or something like infection of the urinary tract. Cat scratch fever, a bacterial infection, sometimes develops symptoms like continuous fever and swollen lymph glands, especially in children, and can persist for months. Doctors are frequently able to verify bacterial infection with blood tests or body scans, and by treatment, they can eliminate the fever.
Certain types of viral infections can also cause chronic fever. Patients who have undiagnosed chronic fatigue syndrome, might have FUO. HIV might also be manifested with a chronic or recurring fever.
There are instances where continuous fever is evidence of diseases that suppress the immune system. Conditions like lupus, juvenile and adult rheumatoid arthritis, and HIV/AIDS result in a fairly constant fever. In these cases, bacterial infection doesn’t need to be actively present, but the body produces fever in response to what it thinks is a constant assault on its immune system. Alternately, illnesses like sarcoidosis may cause the body to respond with a chronic low grade fever.
More serious are certain cancers that may result in chronic fever. Diseases like lymphoma have an effect on the immune system and FUO could be an early symptom. Other forms of cancer may also produce fever.
Sometimes the body responds to injury by developing a fever. If a bone breaks or tissue damage occurs, the body could produce fever as a misdirected healing response and this usually continues until healing is advanced. Alternately, the origin could be another unrelated medical condition like heart disease, occasionally blood pressure conditions, or infections in the heart like bacterial endocarditis, which compromise its function.
Imbalance in some of the body’s hormones may also result in chronic fever. When people have conditions like hyperthyroidism, where they produce too much thyroid hormone, they may run fevers. This condition is easy to verify with blood testing.
A generally more benign cause of a chronic fever is reaction to certain medications. Some people can continue to take medications but might run a slight fever when they use certain kinds. For other patients, fever from medicines might represent severe issues. If fever is burdensome or problematic, medications could be switched or discontinued.