Which of the following three conditions are the most common causes of fever of unknown origin (FUO)?

Fever of unknown origin (FUO) is a clinical situation where a patient's fever remains unexplained after thorough evaluation. The most common causes of FUO typically fall into three major categories: infection, malignancy (cancer), and autoimmune diseases.

Infection is a primary consideration, as numerous infectious diseases can present with FUO, especially those that might not display typical symptoms or laboratory findings. This can include conditions such as endocarditis or deep tissue infections.

Malignancies, particularly hematological cancers like lymphomas and leukemias, are also common etiologies of FUO. They may present with constitutional symptoms, including fever, without any localized findings that might suggest an alternative diagnosis.

Autoimmune diseases, including conditions like systemic lupus erythematosus and rheumatoid arthritis, can also cause elevated body temperatures due to systemic inflammation.

The other options propose alternative conditions, but these do not encapsulate the most prevalent causes associated with FUO. While heart disease, trauma, and pneumonia can cause fever, they are typically accompanied by more definitive clinical findings that lead to a diagnosis. Additionally, gastrointestinal issues, medication side effects, and allergies are generally less common causes of prolonged fever compared to the group of infection, cancer, and autoimmune disorders, which