Fever, Fatigue, Prolonged Infections, and Diagnostic Tests

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Fever, Prolonged Fatigue, and Laboratory Evaluation Processes

Among the most common complaints we hear from patients in our clinical practice are persistent fevers that refuse to subside for weeks and an unexplained sense of fatigue that paralyzes daily life. These symptoms may be a sign of a sneaky infection or a systemic problem silently progressing within the body.

Fever, Fatigue, Prolonged Infections, and Laboratory Tests

Management of Fever of Unknown Origin (FUO)

In medicine, the term "Fever of Unknown Origin" is used to describe febrile conditions with a temperature above 38.3°C that last longer than three weeks and for which the cause cannot be identified during routine examinations. In these cases, an infectious disease specialist works much like a researcher. Insidious conditions such as hidden abscesses, heart valve infections (endocarditis), bone infections (osteomyelitis), or tuberculosis are screened for using advanced imaging studies (MRI, PET-CT) and detailed blood cultures.

Persistent Fatigue and Undiagnosed Viral Infections

Chronic fatigue that persists despite adequate sleep and nutrition is often caused by past or active latent infections. Systemic fatigue caused by specific diseases such as Epstein-Barr Virus (kissing disease), Cytomegalovirus (CMV), Brucella (cheese disease), or Crimean-Congo Hemorrhagic Fever is diagnosed through specific serological blood tests and treated by supporting the patient’s immune system.

Diagnostic Tests and Laboratory Evaluation

There is no room for guesswork in modern infectious disease diagnosis. Our diagnostic and laboratory methods include the following:

Click here for details on microbiological cultures and antibiotic susceptibility testing

Samples taken from blood, urine, wounds, sputum, or stool are cultured on special media in a laboratory setting to monitor the growth of microorganisms. When the causative bacterium is identified, an "antibiogram" test is performed to determine which antibiotics the bacterium is resistant to and which it is sensitive to, thereby ensuring the success of treatment.

Click here for detailson PCR (Molecular Diagnostics) and Serology

Serological blood tests are performed to detect antibodies produced by the body against viruses that do not replicate in cell cultures (such as HIV, hepatitis, COVID-19, and influenza). Using the PCR method—the most advanced technology in modern medicine—the microorganism’s genetic code (DNA/RNA) is directly detected, providing the fastest and most reliable diagnosis within hours.

This content was prepared by Egemed Hospitals.

Published: April 9, 2026 - 12:23 AM • Last Updated: April 9, 2026