Infective endocarditis (IE) is a serious, life-threatening infection involving the endocardial surface of the heart, most commonly the valves. Timely diagnosis is essential due to the high morbidity and mortality associated with complications like embolism, heart failure, and sepsis.
Given the nonspecific and often subtle presentation of IE, clinicians rely on the Duke Criteria—a standardized set of major and minor criteria—to establish a definitive or possible diagnosis. To simplify this complex list, the mnemonic:
BEE FEVEER
serves as a powerful memory aid to retain the diagnostic framework.
This article provides a complete breakdown of Duke's Criteria, pathophysiology of infective endocarditis, clinical relevance, investigation, and management strategies.
What is Infective Endocarditis?
Infective endocarditis is an infection of the endocardium, usually involving one or more heart valves, and is characterized by the formation of vegetations composed of fibrin, platelets, microorganisms, and inflammatory cells.
Commonly Affected Sites:
- Mitral valve (most common overall)
- Tricuspid valve (IV drug users)
- Prosthetic valves
Pathogens:
- Staphylococcus aureus – acute IE
- Streptococcus viridans – subacute IE
- Enterococcus species
- HACEK organisms
- Culture-negative IE – due to prior antibiotics or rare organisms
Duke’s Criteria Overview
Originally developed by Durack et al. in the early 1990s and later modified, the Duke criteria help classify infective endocarditis as:
- Definite IE (clinical, pathologic, or microbiologic confirmation)
- Possible IE (partial evidence)
- Rejected IE (alternative diagnosis or resolution without antibiotics)
Diagnosis is made using a combination of major and minor criteria.
Mnemonic: BEE FEVEER
This creative mnemonic simplifies the memorization of Duke’s criteria.
| Letter | Meaning | Category |
|---|---|---|
| B | Blood culture positive >2 times | Major |
| E | Endocardial involvement (on echo) | Major |
| E | Echo findings – vegetations, abscess, etc. | Major |
| F | Fever >38°C | Minor |
| E | Echocardiogram suggestive but not definitive | Minor |
| V | Vascular phenomena | Minor |
| E | Evidence from microbiology (1 positive) | Minor |
| E | Elevated risk factors (IV drugs, valves) | Minor |
| R | Risk factors – IV drug use, valvular disease | Minor |
Now let’s unpack each component in greater detail.
MAJOR Criteria (BEE)
B – Blood Culture Positive (≥2 times, ≥12 hours apart)
To fulfill the major criterion:
- Positive blood cultures for typical organisms consistent with IE
- Drawn at least 12 hours apart
- Or persistently positive in ≥3 of 4 blood cultures
Typical IE Pathogens:
- Viridans streptococci
- Staphylococcus aureus
- Enterococcus spp.
- HACEK group: Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella
E – Endocardial Involvement from Echocardiography
This refers to visualization of infective lesions on the heart valves via echocardiography.
Positive Echo Findings:
- Vegetations (mobile masses on valves)
- Abscess formation
- Prosthetic valve dehiscence
- New valvular regurgitation
Preferred Modality:
- Transesophageal echocardiography (TEE) is more sensitive than TTE.
E – Echo Findings (Vegetations, Abscess, Dehiscence)
This is essentially the same as the second "E" in the visual mnemonic and underscores the significance of echocardiographic changes. It forms a cornerstone in diagnosis and is often coupled with positive blood cultures.
MINOR Criteria (FEVEER)
F – Fever ≥38°C
Fever is the most common symptom of IE and may be:
- Intermittent or continuous
- Low-grade or high-grade
E – Echo Findings (Suggestive but not definitive)
Subtle findings that may not fulfill major criteria but support the diagnosis.
Examples:
- Small or immobile vegetations
- Indeterminate shadows on echocardiogram
V – Vascular Phenomena
These result from embolization of vegetations or immune responses.
Examples:
- Janeway lesions (non-tender, palms/soles)
- Splinter hemorrhages
- Arterial emboli (stroke, infarcts)
- Mycotic aneurysm
- Conjunctival hemorrhages
E – Evidence from Microbiology (Non-persistent positive)
Single positive culture or serological evidence of atypical organisms:
- Coxiella burnetii
- Brucella
- Bartonella
May also include culture-negative endocarditis diagnosed via serologic or molecular methods.
E – Elevated Risk Factors
Important predisposing conditions:
- IV drug use
- Previous IE
- Prosthetic heart valves
- Congenital heart disease
- Rheumatic valve disease
R – Risk Factors (Drug use, Valvular disease)
A reinforcement of the previous criterion, helping you remember that valvular abnormalities, IV drug abuse, or recent dental/surgical procedures raise suspicion.
Interpreting Duke’s Criteria
| Diagnosis | Requirements |
|---|---|
| Definite IE | 2 Major OR 1 Major + 3 Minor OR 5 Minor |
| Possible IE | 1 Major + 1 Minor OR 3 Minor |
| Rejected IE | Alternate diagnosis confirmed or resolution without Rx |
Clinical Presentation of Infective Endocarditis
| System | Common Symptoms and Signs |
|---|---|
| General | Fever, chills, night sweats, weight loss |
| Cardiac | New murmur, CHF signs, valvular insufficiency |
| Skin | Petechiae, Janeway lesions, Osler nodes |
| Ocular | Roth spots (retinal hemorrhages) |
| CNS | Stroke, meningitis, confusion |
| Musculoskeletal | Myalgias, arthralgias, back pain |
Investigations
Blood Tests:
- CBC: normocytic anemia, leukocytosis
- Elevated ESR, CRP
- Blood cultures (multiple sets before antibiotics)
Imaging:
- Echocardiography (TEE > TTE)
- Chest X-ray (pulmonary edema in left-sided IE)
- MRI brain (stroke from septic emboli)
Other:
- Urinalysis: hematuria, RBC casts (glomerulonephritis)
- Serology for culture-negative pathogens (Q fever, Bartonella)
Complications of Infective Endocarditis
| Type | Examples |
|---|---|
| Cardiac | Heart failure, valvular regurgitation |
| Neurological | Stroke, mycotic aneurysms |
| Renal | Glomerulonephritis, infarction |
| Septic Emboli | Lung abscess, splenic infarction |
| Immunological | Roth spots, Osler nodes, GN |
Treatment Overview
Empirical Antibiotic Therapy
Start after drawing blood cultures
Common empirical regimens:
- Native Valve IE: Ceftriaxone + Vancomycin
- Prosthetic Valve IE: Vancomycin + Gentamicin + Rifampicin
- Adjust based on culture and sensitivity
Duration:
- Usually 4–6 weeks IV therapy
Surgery Indications:
- Valve dysfunction with heart failure
- Uncontrolled infection (abscess, fistula)
- Large vegetations >10 mm with embolic risk
- Prosthetic valve endocarditis
Prevention of IE
Prophylaxis Guidelines (AHA/ESC):
Recommended for high-risk individuals undergoing dental procedures:
- Prosthetic cardiac valves
- Previous history of IE
- Certain congenital heart diseases
Prophylactic Antibiotic: Amoxicillin 2g 1 hour before procedure (or clindamycin for penicillin allergy)
Summary Table: Duke’s Criteria (Mnemonic - BEE FEVEER)
| Category | Criteria | Description |
|---|---|---|
| Major | B – Blood culture positive (≥2, ≥12 hrs apart) | Typical IE organisms in multiple cultures |
| Major | E – Endocardial involvement | Vegetation, abscess, or dehiscence on echo |
| Major | E – Echo findings | New regurgitation or intracardiac mass |
| Minor | F – Fever | ≥38°C |
| Minor | E – Echo (non-definitive findings) | Small vegetations, uncertain echo changes |
| Minor | V – Vascular phenomena | Emboli, Janeway lesions, hemorrhages |
| Minor | E – Evidence from microbiology (1 positive) | Single positive blood culture |
| Minor | E – Elevated risk factors | Prosthetic valve, IV drug use, congenital heart disease |
| Minor | R – Risk factors (repetition) | Reinforces predisposition categories |
Frequently Asked Questions (FAQs)
Q1: What is the most sensitive test for diagnosing IE?
A: Transesophageal echocardiography (TEE) is the most sensitive imaging modality for detecting vegetations and abscesses.
Q2: Can a single positive blood culture meet Duke’s major criteria?
A: No. Major criterion requires ≥2 positive cultures with typical organisms, taken 12 hours apart.
Q3: Which side of the heart is affected in IV drug users?
A: Tricuspid valve (right-sided endocarditis)
Q4: What does “culture-negative endocarditis” mean?
A: No pathogen grows in standard cultures, usually due to prior antibiotics or fastidious organisms like Coxiella, Bartonella.
Q5: What is the hallmark skin sign of infective endocarditis?
A: Janeway lesions (non-tender, vascular phenomena) and Osler nodes (tender, immunologic).
