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Probability diagnosis

Pyogenic abscess (anywhere e.g. liver, pelvis)

Pneumonia (viral, bacterial, atypical)

Epstein–Barr mononucleosis

Viral upper respiratory tract infection

Urinary infection (incl. chronic pyelonephritis)

Serious disorders not to be missed


  • vasculitides (polyarteritis nodosa, giant cell arteritis/polymyalgia)



  • malaria and other tropical diseases

  • zoonoses (e.g. leptospirosis, Q fever, listeriosis)

  • typhoid/paratyphoid fever

  • tuberculosis

  • osteomyelitis

  • chronic septicaemia/bacteraemia

  • infective endocarditis

    • Lyme disease

    • Syphilis (secondary)


  • lymphoma and leukaemia

  • solid cancers (e.g. lung, kidney)

  • disseminated


  • inflammatory bowel disease (e.g. Crohn)

Pitfalls (often missed)

Connective tissue disorder (e.g. rheumatoid arthritis, systemic lupus erythematous)


Drug idiosyncrasies


  • factitious fever

Note: Up to 20% remain unknown. FUO is fever < 38.3°C for at least 3 weeks.

Key history

Include past history, occupation, travel history, sexual history, IV drug use (leads to endocarditis and abscesses), animal contact, medication and other relevant factors. Enquire about associated symptoms such as pruritus, a skin rash, abdominal pain and diarrhoea, and weight loss. Note the fever pattern. The history may need to be repeated.

Key examination

  • Note general features and vital signs

  • Check skin (rash, vesicles or nodules), eyes, temporal arteries, sinuses, teeth and oral cavity, heart (note any murmurs), lungs, abdomen (enlarged or tender liver, spleen, kidney), rectal and pelvic examination, lymph nodes (esp. cervical), urinalysis.

Key investigations

The basics are:

  • FBE


  • CXR and sinus films

  • urine MC

  • routine blood chemistry

  • LFTs

  • blood culture.

Other tests depend on clinical pointers (e.g. specific organisms, lymph node biopsy, HIV, tuberculosis, connective tissue auto-antibodies).

Diagnostic tips

  • Prolonged fever is usually an uncommon presentation of a common disorder (unless recent travel, esp. to tropics).

  • Fever in the elderly is sepsis until proved otherwise (esp. lungs and urinary tract).

  • The diagnosis of septicaemia can be easily missed, especially in small children, the elderly and the immunocompromised.

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