What are the predisposing risk factors for endocarditis of native valves in adults?

Native valve endocarditis in nonintravenous drug users has an identifiable predisposing cardiac lesion in 60-80% of patients, including mitral valve prolapse, degenerative lesions of the aortic and mitral valves, congenital heart disease, and rheumatic heart disease. Rheumatic heart disease was the most common underlying lesion in the past (37-76%) but now accounts for approximately 30% of lesions in adults with endocarditis. Other important risk factors are advanced age, male gender, and diabetes mellitus.

Which congenital heart diseases (CHD) are associated with IE?

CHD accounts for the underlying cardiac lesion in 10-20% of adults with IE. The most common lesions are patent ductus arteriosus, ventricular septal defect, bicuspid aortic valve, coarctation of the aorta, and pulmonic stenosis. With improvement in echocardiographic technology, isolated IE of the pulmonic valve has been increasingly recognized, especially in patients with atrial and ventricular septal defects, patent ductus arteriosus, and tetralogy of Fallot. Additional risk factors for IE are bucuspid aortic valve, especially in men older than 60 years; hypertrophic obstructive cardiomyopathy, which accounts for 5% of adults who develop endocarditis; and Marfan syndrome associated with aortic insufficiency.

What organisms are associated with IE of native valves in patients who are not intravenous drug users?

In patients who are not intravenous drug users the majority of cases of IE are due to

Streptococci (50-70%) (alpha-hemolytic and S. viridans account for the majority)

Staphylococci (25%) (especially S. aureus)

Enterococci (10%)

Native valve infections due to Staphylococcus epidermidis, enteric bacilli, or fungi are uncommon.

Intravenous drug users are at high risk for IE. Describe the course of IE in this subgroup of patients.

Bacteremias in intravenous drug users are common, and the organisms most frequently originate on the skin. Staphylococcus aureus is the most common organism in IE (50-60%), whereas various species of streptococci and enterococci account for approximately 20% of cases; gram-negative bacilli, especially Pseudomonas and Serratia spp., for 10-15%; and fungi, usually culture-negative, for approximately 5% of cases. Infection still shows a slightly higher preference for the tricuspid valve (44%), followed by the mitral (43%), aortic (40%), and pulmonic (3%) valves; infection also may involve both right- and left-sided valves (16%) or both left-sided valves (13%). The majority of patients with IE of the tricuspid valve (70-100%) have pneumonia or multiple septic emboli, and the majority of intravenous drug users with S. aureus (70-80%) have isolated IE of the tricuspid valve.

Endocarditis of the tricuspid valve with large mobile vegetation.

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