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Culture-Negative Endocarditis Prior Antibiotics — SCE Infectious Diseases MCQ

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ModerateBone & Joint InfectionCulture-Negative Endocarditis Prior AntibioticsSCE Infectious Diseases

A 60-year-old man with a metallic heart valve on Warfarin develops culture-negative endocarditis (CNE). Blood cultures are negative after 7 days of incubation. TOE shows a 12 mm vegetation. He has been on antibiotics (Amoxicillin) from his GP for 2 weeks before cultures were taken. What is the most common cause of culture-negative endocarditis?

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Correct answer: C — Prior antibiotic therapy — preceding antibiotic use is the most common cause of CNE, rendering blood cultures negative; extended culture, serology, and molecular testing (16S rRNA PCR from valve tissue or blood) are needed

Culture-negative endocarditis (CNE) accounts for 5–30% of all endocarditis cases. The most common cause is PRIOR ANTIBIOTIC THERAPY (>60% of CNE cases). Other important causes: fastidious organisms (HACEK — require prolonged incubation), Coxiella burnetii (Q fever), Bartonella species, Tropheryma whipplei, NVS (Abiotrophia/Granulicatella), fungi, and C. acnes. Investigation: extended blood culture incubation (≥14 days), Bartonella/Coxiella serology, 16S rRNA PCR from blood or (ideally) valve tissue if surgery performed.

Reference: ESC 2023 – Endocarditis; BSAC 2012 – CNE investigation