A 52-year-old dairy farmer presents with 3 months of low-grade fever, weight loss, and breathlessness. Echocardiography shows aortic valve vegetations, but three sets of blood cultures after 5 days of incubation show no growth. Serology shows Coxiella burnetii phase I IgG titre greater than 1:800. The most likely diagnosis is:
- A Chronic Q fever endocarditis ✓
- B Streptococcus bovis endocarditis with false-negative cultures
- C Libman-Sacks endocarditis
- D Marantic endocarditis associated with occult malignancy
Correct answer: A. Chronic Q fever endocarditis
Explanation
Chronic Q fever typically manifests as culture-negative endocarditis in patients with prior valve damage or immunocompromise. The diagnostic criterion is a Coxiella burnetii phase I IgG titre exceeding 1:800, reflecting persistent intracellular infection. Acute Q fever shows a predominant phase II antibody response instead. Libman-Sacks and marantic vegetations are sterile and would not explain the markedly elevated phase I titre. Cattle and other livestock are the reservoir relevant to this farmer's exposure.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.