A 55-year-old man presents with fever of 3 weeks duration, weight loss, and a new aortic regurgitation murmur. Three sets of blood cultures remain negative after 5 days. Transoesophageal echocardiogram shows a 12 mm vegetation on the aortic valve. Which organism is the most likely cause of this culture-negative endocarditis in this scenario?

• A Staphylococcus epidermidis
• B Coxiella burnetii ✓
• C Streptococcus pneumoniae
• D Escherichia coli

Explanation

Coxiella burnetii (Q fever) is a leading cause of culture-negative endocarditis, particularly involving prosthetic valves or native aortic valves in patients with prior valvular disease. Bartonella species are another important cause. Prior antibiotic use is the most common overall cause, but for true culture-negative endocarditis without prior antibiotics, Coxiella and Bartonella are the key organisms to consider.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.