Culture-Negative Infective Endocarditis

Blood culture–negative endocarditis (BCNE) is infective endocarditis in which routine blood cultures fail to grow the pathogen. A negative bottle does not mean a sterile valve. It means that the usual recovery method has not established the cause. Two mechanisms account for most cases. The first is antibiotic exposure before blood was collected. Even a short course can suppress growth and obscure the organisms that commonly cause endocarditis, especially methicillin-susceptible staphylococci, streptococci, and enterococci. The patient may still have fever, emboli, a new murmur, valve destruction, or heart failure while cultures remain negative. Because treatment cannot yet be narrowed to the pathogen, outcomes are worse when the diagnosis is delayed or the organism is never identified. The second mechanism is an organism that routine culture does not reliably recover. Important examples include Coxiella burnetii, Bartonella species, Tropheryma whipplei, Brucella species, mycobacteria—including Mycobacterium chimaera—and fungi. These organisms require a different combination of exposure-directed serology, molecular testing, special culture handling, or tissue examination. A third possibility is not infective endocarditis at all. Nonbacterial thrombotic endocarditis can produce sterile vegetations and emboli in...