Infective Endocarditis

Infective endocarditis (IE) is infection of the endocardial surface of the heart, most commonly involving the heart valves. It arises when bacteraemia occurs in a host with predisposing cardiac conditions or risk factors that allow bacteria to adhere to and colonise valve tissue. Bacteraemia is often transient and cleared by the immune system, but bacteria with specific adhesins can bind to fibrin-platelet thrombi or damaged endothelium.

IE is classified as acute or subacute. Acute IE has a rapid onset, commonly affects previously healthy valves, and is caused by virulent organisms such as Staphylococcus aureus. Subacute IE has a slower, insidious onset, typically affects previously damaged valves (e.g., with pre-existing regurgitation or a prosthetic valve), and is caused by less virulent organisms such as viridans streptococci and Staphylococcus epidermidis. S. aureus is the most common overall cause.

Risk factors include structural heart disease (e.g., rheumatic heart disease, bicuspid aortic valve), prosthetic heart valves, intravenous drug use (IVDU), indwelling central venous catheters, and previous IE. Clinical signs include fever, new or changing heart murmur, embolic phenomena (e.g., stroke, splenic infarct, renal infarct), immune-complex deposition (Osler nodes, Janeway lesions, Roth spots), and petechiae.

Diagnosis uses the modified Duke criteria, combining microbiological (blood cultures — typically 3 sets from different sites — and serology) and echocardiographic evidence (vegetation on valve, abscess, new prosthetic valve dehiscence). Treatment requires prolonged bactericidal antibiotics (minimum 4 to 6 weeks IV) to penetrate established vegetations. For S. aureus: flucloxacillin (vancomycin for MRSA). For viridans streptococci: penicillin with or without gentamicin. Surgical valve repair or replacement may be required for haemodynamic compromise, uncontrolled infection, or large vegetations with embolic risk.