Definition of Culture-negative endocarditis:

Culture-negative endocarditis is an infection and inflammation of the lining of one or more heart valves in which no endocarditis-causing germs can be identified on a blood culture. The reason for this is that certain germs just do not grow well in the laboratory setting, or because some patients have previously received antibiotics that keep such germs from growing.

See also:

• Endocarditis
• Infectious endocarditis

Causes, incidence, and risk factors:

Endocarditis is usually a result of a blood infection. Bacteria can enter the bloodstream during certain medical procedures, including dental procedures, and travel to the heart, where it can settle on damaged heart valves.

Existing heart disease and problems with your heart valves make you more likely to develop endocarditis. Risk factors include:

• Artificial heart valves
• Congenital heart disease (atrial septal defect, patent ductus arteriosus, and others)
• Heart valve problems (such as mitral insufficiency)
• History of rheumatic heart disease or previous endocarditis

Intravenous drug users are also at risk for this condition, because dirty needles can cause bacteria to enter the bloodstream.

However, an organism commonly found in the mouth, Streptococcus viridans, can cause endocarditis. This is why dental procedures increase your chances for developing this condition. Such procedures are especially risky for children with congenital heart conditions. As a result, it is common practice for children with some forms of congenital heart disease and adults with certain heart valve conditions to take antibiotics before any dental work.

An estimated 10,000 to 15,000 new cases of endocarditis are diagnosed each year in the United States.