Endocarditis is most likely to occur in people whose cardiac valves are vulnerable to infection. For example, the valves may have been scarred in childhood by rheumatic fever, or are abnormal from birth (bicuspid aortic valve or mitral valve prolapse). Persons with prosthetic valves (valves which have been surgically replaced) are also more prone to having bacteria collect and grow prosthetic "vegetations". Other patients at increased risk for endocarditis are those with previous endocarditis or congenital heart diseases. Intravenous drug users are also at especially high risk of acquiring culture-negative endocarditis from contaminated syringes. In patients with endocarditis there is usually an obvious source of infection, such as an infected intravascular catheter, a dental abscess, or an infected skin lesion. However, in many patients there is no history of infection. An estimated 10,000 to 15,000 new cases of endocarditis are diagnosed yearly in the United States.
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