A 58-year-old man has 6 weeks of low-grade fever, night sweats, and weight loss. Three sets of blood cultures are negative despite prior antibiotics having been stopped. Transthoracic echo shows a vegetation on the aortic valve. Serology for which organism is the most likely to establish the diagnosis?

• A Brucella melitensis
• B HACEK group organisms
• C Coxiella burnetii ✓
• D Neisseria gonorrhoeae

Explanation

Coxiella burnetii (chronic Q fever) is the single most common cause of blood culture negative infective endocarditis worldwide, diagnosed by phase I IgG antibody titres rather than cultures. HACEK organisms are fastidious but are typically recoverable from modern automated blood culture systems within 5 days, so they no longer dominate the culture negative category. Brucella and Neisseria endocarditis are rare.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.