Bacterial infections of the vascular system can be rapidly fatal, or they can smolder for months, causing a gradual decline in health. They are not common, but they are always dangerous. Usually the bacteria are carried into the bloodstream by the flow of lymph from an area of infection in the tissues. Some pathogens multiply in the bloodstream, and they may colonize and form biofilms on structures such as the heart valves or abnormalities in the heart or major arteries.
Endocarditis is the term used for infections of the heart valves or the inner, blood-bathed surfaces of the heart, and it can be acute or subacute. Acute bacterial endocarditis starts abruptly with fever, and usually an infection such as pneumonia is present somewhere else in the body or there is evidence of injected-drug abuse. Virulent species such as Staphylococcus aureus and Streptococcus pneumoniae are usually the cause, and they infect both normal and abnormal heart valves. They can often produce a rapidly progressive disease, often with valve destruction and formation of abscesses in the heart muscle, leading to heart failure. By contrast, subacute bacterial endocarditis is usually caused by organisms with little virulence, and it has a much more protracted course. ■ Streptococcus pneumoniae, p. 576
Septicemia is caused by both Gram-negative and Grampositive bacteria, as well as other infectious agents.
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