Endocarditis is infection and inflammation of the lining of a valve in the heart.

Culture-negative endocarditis is a type of endocarditis in which no causative organisms can be grown in a culture taken from a blood sample. This sometimes occurs when blood cultures are drawn after antibiotic treatment has already been started, or if the culprit organism is a fastidious organism that is difficult to grow in culture media.

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.

Signs of endocarditis include:

• Tachycardia (fast heart rate)
• Fever
• A new heart murmur on cardiac exam

The following tests may be requested:

• An ECG and a chest x-ray.
• A complete blood count (CBC).
• Blood cultures: when certain bacteria called fastidious organisms (Bartonella, Coxiella, Mycobacterium, and germs of the HACEK group) cause the endocarditis, cultures may not grow germs. The identification of responsible germs must then be done with special culture conditions and prolonged incubation time. Often, the diagnosis can only be made based on serological or DNA studies.
• An echocardiogram is used to picture the valves of the heart, to visualize any vegetations, and to evaluate heart function.
• A transesophageal echocardiogram (TEE), a special echocardiogram done by introducing a small probe into the patient's mouth down the esophagus.

Complications of endocarditis include:

• Congestive heart failure
• Perivalvular abscesses
• Intracardiac fistulae (abnormal connections within the heart)
• Emboli (blood clots which can travel through the blood and cause obstructed blood vessels and strokes)

All these complications usually require surgery, either to remove vegetations or abscesses, to repair the valves or to replace them with prostheses.

Patients with mitral valve prolapse, valve prostheses, previous endocarditis, congenital heart diseases, and intravenous use of illegal drugs are at increased risk for endocarditis. Patients at known increased risk for endocarditis should consult their primary physician about the need to receive antibiotics prior to dental or genitourinary procedures (antibiotic prophylaxis).

Intravenous drug users should seek treatment for addiction. If that is not possible, use sterile syringes and clean the injection site before every injection to avoid blood infections leading to endocarditis.

For all patients at risk for endocarditis, maintenance of meticulous dental hygiene is of equal importance to antibiotic prophylaxis in the prevention of endocarditis.