A 58-year-old man with a prosthetic aortic valve has 2 months of low-grade fever and weight loss. Three sets of blood cultures are negative. Serology shows IgG titre to Coxiella burnetii phase I antigen of 1:3200 and to phase II antigen of 1:200. What is the most likely diagnosis?
- A Acute Q fever pneumonia
- B Chronic Q fever endocarditis ✓
- C Q fever granulomatous hepatitis
- D Post-Q fever fatigue syndrome
Correct answer: B. Chronic Q fever endocarditis
Explanation
In chronic Q fever, antibody titres to the phase I antigen of Coxiella burnetii exceed those to the phase II antigen, with an IgG phase I titre above 1:1600 being strongly indicative; the pattern reverses in acute Q fever, where phase II titres predominate. Culture-negative endocarditis on a prosthetic valve is the classic presentation of chronic Q fever. Acute Q fever typically presents as pneumonia or self-limited febrile illness with granulomatous hepatitis, and post-Q fever fatigue syndrome is not associated with high phase I titres.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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