Fever of unknown origin

What is fever of unknown origin?

A fever of unknown origin (FUO) is a fever of at least 38.3°C, lasting more than three weeks or occurring often without explanation.

What are the different types of fever of unknown origin?

There are four classifications of fever of unknown origin:

  1. Classic FOD: This is an unexplained fever that lasts for three weeks. Infections or neoplasms such as leukemia may be the cause. Other disorders that may affect connective tissue may also be the cause.
  2. Nosocomial infection: People often get fever as a result of hospitalization after being admitted for causes other than fever and later begin to develop unexplained fever. The most common causes can be pulmonary embolism, sinusitis, deep vein thrombosis and septic thrombophlebitis (an inflammation affecting the veins).
  3. Immunodeficiency: Occurs in people with compromised immune systems and means they are at increased risk for infections. It usually results in an impaired immune system after chemotherapy treatment.
  4. HIV: the disease itself can cause fever and also makes people more prone to infections that can cause fever.

There are four classifications of fever of unknown origin

What are the symptoms?

Typical symptoms of fever of unknown origin are:

  • Fever greater than 38.3° C in adults or 37.5° C in children
  • Sweating
  • Chills
  • Headaches
  • Body aches or joint pains
  • Tiredness
  • Skin rashes
  • Cough and sore throat
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How is FOD diagnosed?

A fever has to persist long enough to be classified as FOD. First, the physician will ask the patient if he or she has been out of the country, has been exposed to any environmental toxins, or has changed his or her daily environment. He or she will also ask about the patient’s family medical history of diseases such as lymphoma.

Blood tests and physical examinations are performed, as blood tests can detect certain conditions, while the skin is examined for signs of rashes or jaundice. Blood, urine and sputum cultures are tested for bacteria and causative fungi.

If the physician detects a heart murmur or suspects possible endocarditis, an echocardiogram may be required to evaluate the heart. Chest x-rays may be needed to check the lungs.

Treatment for FOD

Treatment for fever of unknown origin depends on the cause. In cases where there is no trace of an underlying cause, nonsteroidal anti-inflammatory drugs and antihistamines may be used, as these drugs help reduce the fever.

People whose fevers stem from an immune deficiency can be treated with broad-spectrum antibiotics. Infections account for 20 to 40 percent of FOD. Those with HIV-associated fevers who are treated with antiviral drugs.