Microbiology Cheat Sheet
Rheumatic Fever vs Endocarditis
Rheumatic fever vs endocarditis for NEET-PG: molecular mimicry, Jones criteria, ASO titre, Aschoff bodies, Duke criteria, S. aureus, and viridans streptococci.
MedNext Academy | 3 min read
Rheumatic Fever vs Endocarditis
Rheumatic fever vs endocarditis for NEET-PG: molecular mimicry, Jones criteria, ASO titre, Aschoff bodies, Duke criteria, S. aureus, and viridans streptococci.
This topic covers the etiologic agents, pathogenesis, and diagnosis of rheumatic fever and infective endocarditis, and the microbial identification of cardiac infection pathogens.
High-yield lines
- Acute rheumatic fever is an immune-mediated sequela of Streptococcus pyogenes pharyngitis, not skin infection, driven by molecular mimicry with cardiac myosin.
- In rheumatic fever the organism is not present in the heart, blood cultures are negative, and diagnosis relies on the Jones criteria plus evidence of antecedent infection.
- Anti-streptolysin O titre is the most widely used serological evidence of preceding GAS pharyngitis, with anti-DNase B as a useful supplement.
- Aschoff bodies in the myocardium are the pathological hallmark of rheumatic carditis, and the mitral valve is most commonly affected.
- Secondary prophylaxis with benzathine penicillin G every 3 to 4 weeks prevents recurrent rheumatic fever and progressive valve damage.
- Staphylococcus aureus is the most common cause of acute infective endocarditis and can infect normal valves.
- Viridans group streptococci are the most common cause of subacute endocarditis on previously damaged valves following dental procedures.
- The modified Duke criteria diagnose definite endocarditis with 2 major, or 1 major plus 3 minor, or 5 minor criteria.
- Three sets of blood cultures from separate venepunctures before antibiotics are essential in suspected endocarditis.
- Streptococcus gallolyticus (formerly S. bovis) endocarditis mandates colonoscopy to exclude colorectal carcinoma.
- S. aureus bacteraemia always warrants echocardiography to exclude endocarditis, even with an identified primary focus.
- In intravenous drug users the tricuspid valve is most commonly affected, with septic pulmonary emboli and S. aureus predominance.
- Culture-negative endocarditis should prompt serology for Coxiella burnetii and Bartonella, and HACEK organisms require prolonged incubation.
- Enterococcus is identified by bile-esculin positivity, growth in 6.5 percent NaCl, and PYR positivity, and requires cell-wall-active plus aminoglycoside synergy.
Mapped competency codes
- MI2.1
- MI2.2
- MI2.3
Continue into the full chapter
This summary maps to MI2-cvs-and-blood.
Frequently Asked Questions
Why are blood cultures negative in rheumatic fever?
Rheumatic fever is immune-mediated through molecular mimicry, not direct bacterial invasion of the heart, so the organism is absent from the valves.
Which organism causes acute versus subacute endocarditis?
Staphylococcus aureus causes acute endocarditis and can attack normal valves, while viridans streptococci cause subacute endocarditis on damaged valves.
What must S. gallolyticus endocarditis prompt?
Colonoscopy to exclude colorectal carcinoma, given the strong association with colonic neoplasia.
What is the pathological hallmark of rheumatic carditis?
Aschoff bodies, perivascular granulomas in the myocardium containing Anitschkow cells with caterpillar nuclei.
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