Infective Endocarditis
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Direct answer
Infective endocarditis is diagnosed by the modified Duke criteria: two major, or one major plus three minor, or five minor criteria. Major criteria are typical organisms in repeated blood cultures (viridans streptococci, Streptococcus gallolyticus, HACEK, Staphylococcus aureus, community-acquired enterococci) and endocardial involvement on echocardiography — vegetation, abscess or new prosthetic dehiscence. Take three sets of blood cultures and a transthoracic echo before antibiotics in stable patients; treat with prolonged organism-directed intravenous bactericidal therapy — four to six weeks for native valves, six for prosthetic. Staphylococcus aureus is now the commonest organism, including in Indian series.
What you must remember
- Duke minor criteria: predisposition (prosthetic valve, previous endocarditis, congenital heart disease, intravenous drug use), fever above 38°C, vascular phenomena (arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial haemorrhage, Janeway lesions), immunological phenomena (Osler nodes, Roth spots, glomerulonephritis, positive rheumatoid factor), and microbiology not meeting major criteria.
- Echo strategy: transthoracic first; transoesophageal for prosthetic valves, negative studies with high suspicion, and suspected complications — a normal echo never excludes endocarditis.
- Organism-context associations: S aureus with acute disease, health-care exposure and right-sided infection in intravenous drug users; viridans streptococci after dental procedures; enterococci after genitourinary or gastrointestinal instrumentation; coagulase-negative staphylococci with early prosthetic valves; culture-negative disease most often from prior antibiotics, plus Coxiella, Bartonella, HACEK, fungi and Brucella.
- Empiric regimens: native valve — vancomycin plus gentamicin (ampicillin-based where enterococcal cover is prioritised); prosthetic — vancomycin plus gentamicin plus rifampicin; definitive therapy follows cultures.
- Surgery — three pillars: heart failure from valve dysfunction (commonest and most urgent), uncontrolled infection (perivalvular abscess, fistula, persistent bacteraemia, fungal or resistant organisms) and embolism prevention (vegetation above 10 mm with an embolic event despite therapy, or very large mobile vegetations).
- Right-sided endocarditis: S aureus in intravenous drug users, presenting with septic pulmonary rather than systemic emboli; shorter courses often suffice and surgery is rarely needed.
- Prophylaxis: restricted to high-risk conditions — prosthetic valve or material, previous endocarditis, selected congenital heart disease — before dental procedures manipulating gingiva or tooth apex; a single pre-procedure dose of amoxicillin or an alternative for allergic patients.
Common confusion
Osler nodes (tender, immunological, on finger pulps) contrast with Janeway lesions (non-tender, haemorrhagic, on palms and soles). Culture-negative endocarditis is mismanaged by simply repeating cultures — the correct response is serology, repeat imaging and PET-CT for prosthetic valves where available. "Subacute" describes indolent viridans disease, while S aureus produces an acute, destructive course — tempo itself is a clue.
Exam-focused takeaway
Stems provide fever with a new murmur plus a predisposing lesion and ask the diagnostic criterion count, the organism, or the next step — classically "three sets of blood cultures before antibiotics". Surgery questions quote heart failure, an abscess or a 12 mm vegetation with a stroke. Prophylaxis questions test the restricted indication list, especially "previous endocarditis". Know the culture-negative organisms as a list and the organism-context pairs.
Frequently asked questions
What constitutes the major Duke criteria?
Typical micro-organisms in repeated blood cultures, persistently positive cultures, or a single positive Coxiella culture, plus echocardiographic endocardial involvement — vegetation, abscess or dehiscence.
Which organisms cause culture-negative endocarditis?
Prior antibiotic exposure (the commonest reason), Coxiella, Bartonella, HACEK organisms, fungi, Brucella and nutritionally variant streptococci.
What are the surgical indications in endocarditis?
Heart failure from valve dysfunction, uncontrolled infection (abscess, persistent bacteraemia, resistant organisms) and prevention of systemic embolism from large or recurrently embolising vegetations.
Who needs antibiotic prophylaxis?
Only high-risk patients — prosthetic valve or material, previous endocarditis, certain congenital lesions — before dental procedures manipulating the gingiva or periapical region.