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Community-Acquired Pneumonia (Severe Criteria) — ABIM Board MCQ

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HardInfectious DiseasesCommunity-Acquired Pneumonia (Severe Criteria)ABIM Board

A 54-year-old livestock veterinarian has six weeks of fever, weight loss, a new aortic regurgitation murmur, splenomegaly, and echocardiographic vegetations. Three blood-culture sets obtained before antibiotics remain negative. Which diagnostic test is most likely to establish the cause?

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Correct answer: B — Phase I Coxiella burnetii IgG serology

The best answer is “Phase I Coxiella burnetii IgG serology”. Subacute culture-negative endocarditis in a patient with livestock exposure strongly suggests Coxiella burnetii. High phase I IgG titers establish chronic Q-fever endocarditis in the appropriate clinical setting. Broad molecular testing can supplement but should not replace the exposure-directed high-yield assay; routine cultures remain negative because Coxiella is intracellular.

Reference: 2023 ESC Guidelines for the Management of Endocarditis (endorsed by infectious-disease experts and applicable to US board practice): https://www.escardio.org/static-file/Escardio/Guidelines/Endocarditis-Guidelines-2023.pdf