Differential Diagnosis for a 29-year-old Male with 2 Weeks of Fever Unresponsive to Antibiotics

• Single Most Likely Diagnosis
  • Viral infection (e.g., influenza, mononucleosis): This is a common cause of prolonged fever in a young adult, especially if the patient has been exposed to others with similar symptoms or has not responded to antibiotics, which are ineffective against viral infections.
• Other Likely Diagnoses
  • Tuberculosis (TB): Although less common in young, otherwise healthy adults, TB can present with prolonged fever and is important to consider, especially if the patient has been exposed to someone with TB or has recently traveled to an area where TB is endemic.
  • Endocarditis: This is an infection of the heart valves and can cause prolonged fever. It's more likely in individuals with a history of heart disease or intravenous drug use, but can occur in anyone.
  • Abscess or infected fluid collection: If the patient has a history of recent surgery, trauma, or an invasive medical procedure, an abscess or infected fluid collection could be causing the fever.
  • Connective tissue disease (e.g., lupus, rheumatoid arthritis): These autoimmune diseases can cause fever and are more common in young adults.
• Do Not Miss Diagnoses
  • Meningitis or encephalitis: Infections of the brain or meninges can present with fever and are medical emergencies. Early diagnosis and treatment are crucial to prevent serious complications or death.
  • Sepsis: Although the patient has not responded to antibiotics, sepsis (a severe, life-threatening response to infection) must be considered, especially if there are signs of organ dysfunction.
  • HIV infection: Fever can be an early symptom of HIV infection, and diagnosing HIV early is critical for effective treatment and prevention of complications.
  • Lymphoma: Certain types of lymphoma can cause prolonged fever, and while less common, this diagnosis should not be missed due to its significant implications for treatment and prognosis.
• Rare Diagnoses
  • Brucellosis: A zoonotic infection that can cause fever, usually in individuals who work with animals or consume unpasteurized dairy products.
  • Leptospirosis: An infection caused by bacteria found in fresh water that has been contaminated with the urine of infected animals, which can cause fever among other symptoms.
  • Histoplasmosis or coccidioidomycosis: Fungal infections that can cause fever, more common in specific geographic areas or in individuals with certain occupational exposures.
  • Whipple's disease: A rare, systemic bacterial infection that can cause fever, malabsorption, and other symptoms, often diagnosed late due to its non-specific presentation.