Culture-negative endocarditis is an infection and inflammation of the lining of one or more heart valves, but in which no endocarditis-causing germs can be found in a routine blood culture. This is because certain germs do not grow well in a laboratory setting, or some people have received antibiotics in the past that keep such germs from growing outside of the body.
Endocarditis is usually a result of a bloodstream infection. Bacteria can enter the bloodstream during certain medical procedures, including dental procedures or through intravenous injection using non-sterile needles. Then bacteria can travel to the heart, where they can settle on heart valves.
Endocarditis (culture-negative)
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Holland TL, Bayer AS, Fowler VG. Endocarditis and intravascular infection. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 80.