Infective Endocarditis
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Direct answer
Definite infective endocarditis by the modified Duke criteria means two major criteria, or one major plus three minor, or five minor — the majors being typical organisms in two separate blood cultures (viridans streptococci, S. gallolyticus, HACEK, community-acquired S. aureus or enterococci; persistent positivity; or a single positive Coxiella) and echocardiographic vegetation, abscess, prosthetic dehiscence or new regurgitation. Staphylococcus aureus has overtaken viridans streptococci as the commonest overall cause, though rheumatic valve disease still underlies much Indian endocarditis. Three blood culture sets from separate sites precede antibiotics; echocardiography is mandatory — transoesophageal for prosthetic valves, negative transthoracic studies or complications. Cure requires weeks of intravenous, bactericidal, culture-guided antibiotics; surgery rescues heart failure from regurgitation, uncontrolled infection and embolising vegetations.
What you must remember
- Modified Duke majors: (1) typical organisms from two separate cultures, or persistently positive cultures at least 12 hours apart, or a single positive Coxiella; (2) echo vegetation, paravalvular abscess, new partial dehiscence of a prosthetic valve; (3) new valvular regurgitation — a worsening murmur alone does not qualify.
- Modified Duke minors: predisposition (prosthetic valve, previous endocarditis, rheumatic or congenital valve disease, injecting drug use), fever above 38 degrees, vascular phenomena (arterial emboli, septic pulmonary infarcts, mycotic aneurysm, Janeway lesions), immunological phenomena (Osler nodes, Roth spots, glomerulonephritis, positive rheumatoid factor), microbiological evidence not meeting a major.
- Possible endocarditis: one major plus one minor, or three minors — a category that triggers repeat cultures and repeat echo.
- Culture-negative organisms: Coxiella, Bartonella, Brucella, fungi and slow-growing HACEK — often the legacy of prior antibiotic courses; Brucella is endemic in northern India.
- Organism-context pairs: viridans after dental procedures, S. gallolyticus demands colonoscopy (colonic neoplasia), enterococci from genitourinary and hepatobiliary sources, S. aureus from skin, lines and injecting drug use.
- Antibiotic spine: four to six weeks intravenous, high-dose, bactericidal and culture-guided — penicillin or ceftriaxone for susceptible streptococci, antistaphylococcal penicillins or vancomycin for staphylococci, with prosthetic-valve courses the longest.
- Surgery triggers: heart failure from regurgitation (the strongest), uncontrolled infection — abscess, persistent bacteraemia, fungal endocarditis — and embolic prevention with large vegetations (above 10 mm with an embolic event, or above 15 mm on some recommendations).
- Non-negotiable habits: every S. aureus bacteraemia gets an echocardiogram; antibiotic prophylaxis covers the highest-risk cardiac lesions before dental procedures.
Where students slip
Three slips recur. First, blood cultures after antibiotics: Indian patients arrive having swallowed leftover antibiotics, sterilising the classic organisms and inflating the culture-negative category — the discipline is three sets from separate sites before therapy, holding empirical antibiotics when the patient is stable. Second, murmur-watching: a change in murmur is a minor criterion, and "no murmur" excludes nothing in tricuspid or prosthetic disease — echo decides. Third, peripheral signs as decoration: Osler nodes and Roth spots are immunologic minors, Janeway lesions vascular minors — examiners ask exactly which list each belongs to. The Indian viva adds Brucella and Salmonella endocarditis in endemic regions, and the practical reality that four weeks of outpatient intravenous therapy needs a line, a plan and a patient who can travel.
Frequently asked questions
What combination makes definite infective endocarditis in the modified Duke criteria?
Two major criteria, one major plus three minor, or five minor — with possible endocarditis defined as one major plus one minor or three minor.
Which organism is now commonest overall?
Staphylococcus aureus — overtaking viridans streptococci, dominating healthcare-associated and injecting-drug-use endocarditis.
Why three blood culture sets before antibiotics?
Separate-site, temporally spaced sets confirm persistence, exclude contamination and improve yield — and prior antibiotic pills are the commonest cause of culture-negative endocarditis in India.
When is transoesophageal echo preferred?
Prosthetic valves, suspected abscess or complications, negative transthoracic studies with ongoing suspicion, and Staphylococcus aureus bacteraemia.
What is the strongest indication for surgery during endocarditis?
Heart failure from valve destruction or regurgitation — ahead of uncontrolled infection (abscess, persistent bacteraemia, fungi) and embolic prevention with large vegetations.