What are the diagnostic criteria and treatment guidelines for endocarditis?

Diagnostic Criteria and Treatment Guidelines for Infective Endocarditis

The diagnosis of infective endocarditis (IE) should be based on the modified Duke criteria with the 2015 ESC updates, which include blood culture findings, echocardiographic evidence, and clinical manifestations, while treatment should be guided by the identified causative organism with specific antimicrobial regimens. 1

Diagnostic Criteria

Modified Duke Criteria with 2015 ESC Updates

Pathological Criteria

• Microorganisms demonstrated by culture or histological examination of a vegetation, embolized vegetation, or intracardiac abscess specimen 1
• Pathological lesions showing active endocarditis (vegetation or intracardiac abscess) by histological examination 1

Clinical Criteria for Definite IE

• 2 major criteria; or
• 1 major criterion and 3 minor criteria; or
• 5 minor criteria 1

Major Criteria

1. Blood cultures positive for IE:

   • Typical microorganisms from 2 separate blood cultures: viridans streptococci, Streptococcus gallolyticus (S. bovis), HACEK group, Staphylococcus aureus, or community-acquired enterococci without primary focus 1
   • Persistently positive blood cultures: ≥2 positive cultures drawn >12h apart or majority of ≥4 separate cultures with first and last drawn ≥1h apart 1
   • Single positive blood culture for Coxiella burnetii or phase I IgG antibody titer >1:800 1, 2

2. Imaging positive for IE:

   • Echocardiogram showing vegetation, abscess, pseudoaneurysm, intracardiac perforation, new partial dehiscence of prosthetic valve, or new valvular regurgitation 1
   • Paravalvular lesions identified by cardiac CT (2015 ESC update) 1
   • Abnormal activity around prosthetic valve implantation site detected by 18F-FDG PET/CT (if prosthesis implanted >3 months) or radiolabelled leukocyte SPECT/CT (2015 ESC update) 1

Minor Criteria

1. Predisposition: predisposing heart condition or injection drug use 1
2. Fever: temperature ≥38°C 1
3. Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhages, conjunctival hemorrhages, Janeway lesions 1
4. Immunologic phenomena: glomerulonephritis, Osler's nodes, Roth's spots, rheumatoid factor 1
5. Microbiological evidence: positive blood culture not meeting major criteria or serological evidence of active infection with organism consistent with IE 1
6. Recent embolic events or infectious aneurysms identified by imaging only (2015 ESC update) 1

Diagnostic Challenges and Pitfalls

• Modified Duke criteria show lower diagnostic accuracy for early diagnosis in prosthetic valve endocarditis (PVE) and cardiac device-related IE, with echocardiography being inconclusive in up to 30% of cases 1
• Blood culture-negative IE (BCNIE) often results from prior antibiotic administration, highlighting the need to withdraw antibiotics and repeat blood cultures 1, 3
• Advanced imaging techniques (cardiac CT, cerebral MRI, 18F-FDG PET/CT) can improve detection of endocardial lesions and extracardiac complications in difficult cases 1

Treatment Guidelines

Microbiological Diagnosis Approach

1. Obtain at least three sets of blood cultures before starting antibiotics 1
2. For culture-negative cases, consider:
   • Serological testing for Coxiella burnetii, Bartonella spp., Aspergillus spp., Mycoplasma pneumonia, Brucella spp., and Legionella pneumophila 1
   • PCR testing of surgical material when available 1
   • Specialized culture techniques for fastidious organisms 1

Antimicrobial Therapy

Treatment should be guided by the identified causative organism 1:

1. Streptococcal IE (viridans group, S. bovis):

   • Aqueous crystalline penicillin G sodium (12-18 million U per 24h IV) or ceftriaxone (2g per 24h IV/IM) for 4 weeks 1

2. Staphylococcal IE:

   • Native valve: anti-staphylococcal penicillin or cefazolin for methicillin-sensitive S. aureus; vancomycin for methicillin-resistant strains 1
   • Prosthetic valve: more prolonged therapy often with combination antibiotics 1

3. Enterococcal IE:

   • Combination therapy with ampicillin/penicillin plus gentamicin 1

4. HACEK organisms:

   • Ceftriaxone or another third-generation cephalosporin 1

5. Fungal IE:

   • Antifungal therapy plus surgical intervention 1

Surgical Considerations

Surgical intervention should be considered in cases with:

• Heart failure due to valve dysfunction 1
• Uncontrolled infection (abscess, persistent bacteremia) 1
• Prevention of embolic events (large vegetations) 1
• Prosthetic valve endocarditis, especially early-onset cases 1

Important Clinical Considerations

• Early diagnosis is crucial for improved outcomes, with mortality rates remaining high (15-30%) despite advances in treatment 3
• Echocardiography plays a central role in diagnosis, with transesophageal echocardiography (TEE) recommended when transthoracic echocardiography is negative but clinical suspicion remains high 1
• The sensitivity of the modified Duke criteria is approximately 80% when evaluated at the end of patient follow-up, but may be lower during early clinical assessment 1, 3
• Antibiotic prophylaxis recommendations have become more restrictive in recent guidelines, focusing only on highest-risk patients 1