health

Viruses, fungi, or other microscopic organisms can all cause infectious
endocarditis, but the disease usually arises from a bacterial infection.
A common bacterium abundant in the oral cavity, Streptococcus viridans
(strep-tuh-KAH-kus VEER-ih-danz), is responsible for up to half of all
cases of bacterial endocarditis. Other bacterial culprits include bacteria
from the staphylococcus, streptococcus, and enterococcus families and,
less commonly, other types.
In most cases of infectious endocarditis, bacteria that normally live harmlessly
on the body, such as in the mouth, on the skin, in the intestines, or in
the urinary tract (YOOR-ih-nair-e TRAKT), enter the blood (a condition
known as bacteremia, bak-tuh-REE-me-uh). The bacteria can enter tissues
through a cut or a tear that has resulted from a dental or medical procedure,
or they may enter the blood because of a site of an infection somewhere else
in the body. Additionally, intravenous drug users are at high risk for infectious
endocarditis, as staphylococcus bacteria in skin have many opportunities
to enter the bloodstream through broken skin. Once in the bloodstream,
the bacteria travel to the heart and may stick to the endocardium or heart
valves. As they grow and multiply, the bacteria may become entangled in
vegetations, which are composed of clumps of platelets; bacteria; red and
white blood cells; and fibrin, a protein that helps blood clot.