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Harvard Medical School

Endocarditis

What Is It?

Endocarditis, also called infective endocarditis, is an infection and inflammation of the heart valves and the inner lining of the heart chambers, which is called the endocardium. Endocarditis occurs when infectious organisms, such as bacteria or fungi, enter the bloodstream and settle in the heart. In most cases, these organisms are streptococci ("strep"), staphylococci ("staph") or species of bacteria that normally live on body surfaces. The infecting organism enters the bloodstream through a break in the skin caused by a skin disorder or injury; a medical or dental procedure; or a skin prick, especially among intravenous drug users.

Depending on the aggressiveness (virulence) of the infecting germ, the heart damage caused by endocarditis can be swift and severe (acute endocarditis) or slower and less dramatic (subacute endocarditis).

• Acute endocarditis - Acute endocarditis most often occurs when an aggressive species of skin bacteria, especially a staphylococcus, enters the bloodstream and attacks a normal, undamaged heart valve. Once staph bacteria begin to multiply inside the heart, they may send small clumps of bacteria called septic emboli into the bloodstream to spread the infection to other organs, especially to the kidneys, lungs and brain. Intravenous (IV) drug users are at very high risk of acute endocarditis, because numerous needle punctures give aggressive staph bacteria many opportunities to enter the blood through broken skin. Dirty drug paraphernalia increases the risk. If untreated, this form of endocarditis can be fatal in less than six weeks.

• Subacute endocarditis - This form of endocarditis most often is caused by one of the viridans group of streptococci (Streptococcus sanguis, mutans, mitis or milleri) that normally live in the mouth and throat. Streptococcus bovis or Streptococcus equinus also can cause subacute endocarditis, typically in patients who have some form of gastrointestinal cancer, usually colon cancer. Subacute endocarditis tends to involve heart valves that already are damaged in some way, and it usually is less likely to cause septic emboli than acute endocarditis. If untreated, subacute bacterial endocarditis can worsen for as long as one year before it is fatal.

Endocarditis strikes approximately 19,000 people in the United States each year, with 2,000 deaths. Men develop endocarditis more often than women, and the illness is more common among people who have one or more of the following risk factors:

• A congenital (present at birth) malformation of the heart or a heart valve, or mitral valve prolapse with mitral valve regurgitation

• A heart valve damaged by rheumatic fever or by age-related valve thickening with calcium deposits

• An implanted device in the heart (pacemaker wire, artificial heart valve)

• A history of IV drug use

• A chronic (long-term) medical condition that weakens the immune system (alcoholism, diabetes, cancer with chemotherapy)

In about 20% to 40% of patients who do not have artificial heart valves and who do not use intravenous drugs, no heart problem can be identified that would increase their risk of endocarditis. In the 10% to 20% of endocarditis patients who have artificial heart valves, infections that follow within 60 days of valve surgery often are caused by a staphylococcus, while endocarditis that occurs later most frequently is caused by a streptococcus.

Endocarditis, also called infective endocarditis, is an infection and inflammation of the heart valves and the inner lining of the heart chambers, which is called the endocardium. Endocarditis occurs when infectious organisms, such as bacteria or fungi, enter the bloodstream and settle in the heart. In most cases, these organisms are streptococci ("strep"), staphylococci ("staph") or species of bacteria that normally live on body surfaces. The infecting organism enters the bloodstream through a break in the skin caused by a skin disorder or injury; a medical or dental procedure; or a skin prick, especially among intravenous drug users.

Depending on the aggressiveness (virulence) of the infecting germ, the heart damage caused by endocarditis can be swift and severe (acute endocarditis) or slower and less dramatic (subacute endocarditis).

• Acute endocarditis - Acute endocarditis most often occurs when an aggressive species of skin bacteria, especially a staphylococcus, enters the bloodstream and attacks a normal, undamaged heart valve. Once staph bacteria begin to multiply inside the heart, they may send small clumps of bacteria called septic emboli into the bloodstream to spread the infection to other organs, especially to the kidneys, lungs and brain. Intravenous (IV) drug users are at very high risk of acute endocarditis, because numerous needle punctures give aggressive staph bacteria many opportunities to enter the blood through broken skin. Dirty drug paraphernalia increases the risk. If untreated, this form of endocarditis can be fatal in less than six weeks.

• Subacute endocarditis - This form of endocarditis most often is caused by one of the viridans group of streptococci (Streptococcus sanguis, mutans, mitis or milleri) that normally live in the mouth and throat. Streptococcus bovis or Streptococcus equinus also can cause subacute endocarditis, typically in patients who have some form of gastrointestinal cancer, usually colon cancer. Subacute endocarditis tends to involve heart valves that already are damaged in some way, and it usually is less likely to cause septic emboli than acute endocarditis. If untreated, subacute bacterial endocarditis can worsen for as long as one year before it is fatal.

Endocarditis strikes approximately 19,000 people in the United States each year, with 2,000 deaths. Men develop endocarditis more often than women, and the illness is more common among people who have one or more of the following risk factors:

• A congenital (present at birth) malformation of the heart or a heart valve, or mitral valve prolapse with mitral valve regurgitation

• A heart valve damaged by rheumatic fever or by age-related valve thickening with calcium deposits

• An implanted device in the heart (pacemaker wire, artificial heart valve)

• A history of IV drug use

• A chronic (long-term) medical condition that weakens the immune system (alcoholism, diabetes, cancer with chemotherapy)

In about 20% to 40% of patients who do not have artificial heart valves and who do not use intravenous drugs, no heart problem can be identified that would increase their risk of endocarditis. In the 10% to 20% of endocarditis patients who have artificial heart valves, infections that follow within 60 days of valve surgery often are caused by a staphylococcus, while endocarditis that occurs later most frequently is caused by a streptococcus.