Infective Endocarditis
Infection of the endocardium, typically involving heart valves, causing fever, embolic phenomena, and heart failure. *Staphylococcus aureus* and oral streptococci are common; diagnosis integrates blood cultures and echocardiography; treatment is prolonged high-dose bactericidal antibiotics and sometimes surgery.
Key Facts
Key points
- Modified Duke criteria integrate major/minor clinical, microbiological, and imaging features.
- Three sets of blood cultures before antibiotics (different sites, 30 minutes apart) unless critically unwell.
- Empirical IV therapy if unstable: often flucloxacillin 2 g IV 4-hourly (or vancomycin if MRSA risk) plus gentamicin only when synergy indicated (e.g. streptococcal native valve) — seek local protocol.
- Native valve streptococcal IE: benzylpenicillin 2.4 g IV 4-hourly (or ceftriaxone) plus short-course gentamicin synergy in selected cases per guideline.
- MRSA: vancomycin IV (monitor levels) or daptomycin in right-sided IE when appropriate.
- Indications for surgery: heart failure, uncontrolled infection, embolic events, perivalvular abscess/fistula.
Overview
Epidemiology and risk
Incidence peaks in older adults and in people with prosthetic valves, prior endocarditis, injection drug use, or rheumatic valve disease.
Pathogenesis
Endothelial damage allows platelet–fibrin deposition; transient bacteraemia seeds vegetations. Biofilm on prosthetic material complicates eradication.
Organisms
- Native valves: viridans streptococci, S. aureus, enterococci.
- Prosthetic early: coagulase-negative staphylococci, S. aureus.
- IVDU: S. aureus (often right-sided).
Clinical Presentation
Features
- Fever, night sweats, malaise, new murmur (or change), splinter haemorrhages, Osler nodes, Janeway lesions, Roth spots (classic but not sensitive).
Embolic and systemic
- Stroke, limb ischaemia, splenic/renal infarcts, mycotic aneurysm.
Prosthetic valve
- Paravalvular leak, heart block (abscess), persistent fever.
Differential Diagnosis
| Diagnosis | Clues |
|---|---|
| Non-infective marantic endocarditis | Malignancy, TTE/TOE vegetation morphology |
| Acute rheumatic fever | Migratory arthritis, chorea, recent strep |
| Atrial myxoma | Tumour plop, echo mass |
| Q fever/Coxiella IE | Culture-negative, serology, travel/animal exposure |
| Libman–Sacks (SLE) | Autoantibodies, clinical context |
Diagnosis / Investigation
Microbiology
- ≥3 blood culture sets from peripheral sites.
- If culture-negative: consider Coxiella, Bartonella, HACEK, fungi — specialist lab advice.
Cardiac imaging
- TTE first; TOE if prosthetic valves, suspected complications, or negative TTE with high suspicion.
Other
- ECG (heart block), CT if abscess/embolic stroke assessment, CRP/FBC, renal function before nephrotoxic agents.
Management
Empirical (before sensitivities — follow local guideline)
Example combinations (adjust renal function):
- Flucloxacillin 2 g IV 4-hourly + gentamicin synergy only when indicated.
- Vancomycin IV (loading per protocol) if MRSA risk or penicillin anaphylaxis (consult microbiology).
Streptococcal native valve (example)
- Benzylpenicillin 2.4 g IV 4-hourly or ceftriaxone 2 g IV OD; duration commonly 4–6 weeks depending on organism and complications.
Staphylococcus aureus
- Flucloxacillin 2 g IV 4-hourly (native); longer courses for prosthetic/right-sided disease per guideline.
Enterococcal
- Amoxicillin or ampicillin based regimens ± gentamicin synergy — nephrotoxicity risk; alternative: ceftriaxone + ampicillin for certain E. faecalis.
Surgery
- Heart failure, refractory infection, abscess, embolic stroke with large vegetation — MDT decision.
Antibiotic prophylaxis (UK)
- Routine dental prophylaxis not recommended solely for IE in most patients; manage specific high-risk groups per NICE.
Prognosis
In-hospital mortality remains substantial, especially with S. aureus, heart failure, and neurological complications. Surgical treatment improves outcomes in selected cases. Long-term follow-up for valve dysfunction is essential.
Other Relevant Information
Gentamicin synergy
Use only with clear indication and monitor levels and renal function; many centres shorten aminoglycoside exposure due to toxicity.
Outpatient OPAT
Selected stable patients may complete IV therapy via OPAT services.