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Blood Culture-Negative Endocarditis — EECC MCQ

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HardValvular Heart DiseaseBlood Culture-Negative EndocarditisEECC

A 45-year-old woman with a prosthetic mitral valve presents with suspected IE but initial blood cultures are negative after 5 days of incubation. She has been on oral antibiotics (amoxicillin) for a dental abscess prior to presentation. What is the next diagnostic step for blood culture-negative endocarditis (BCNE)?

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Correct answer: B — Extended serology panel for fastidious organisms (Coxiella burnetii, Bartonella, Brucella, Tropheryma whipplei) and molecular testing (16S rRNA PCR) on blood or surgical tissue

Blood culture-negative endocarditis (BCNE) accounts for 5-10% of IE cases. The most common cause is prior antibiotic exposure (which suppresses growth of common organisms). Other causes include fastidious organisms that require special culture conditions or serological diagnosis. The 2023 ESC IE Guidelines recommend a systematic workup for BCNE: (1) extended incubation of blood cultures (>5 days); (2) serology for Coxiella burnetii (Q fever — most common BCNE organism in some series), Bartonella species, Brucella, Mycoplasma, Legionella; (3) molecular testing (broad-range 16S rRNA PCR on blood or excised valve tissue); (4) consider fungi (Aspergillus, Candida) with beta-D-glucan and galactomannan testing. Valve tissue analysis (histology, culture, PCR) at surgery provides the highest diagnostic yield.

Reference: ESC (2023): Guidelines on Infective Endocarditis