Subacute Bacterial Endocarditis (Viridans group streptococci)
Overview
Plain-Language Overview
Subacute Bacterial Endocarditis (SBE) is an infection that affects the heart valves, which are crucial for maintaining proper blood flow through the heart. It is caused by bacteria, most commonly the viridans group streptococci, which enter the bloodstream and attach to damaged areas of the heart valves. This infection develops slowly over weeks to months and can cause symptoms like fever, fatigue, and heart murmurs. The infection can damage the valves, leading to problems with heart function and potentially serious complications such as heart failure or stroke. Early detection and treatment are important to prevent these complications and protect heart health.
Clinical Definition
Subacute Bacterial Endocarditis (SBE) is a form of infective endocarditis characterized by a slowly progressive infection of the heart valves, typically caused by viridans group streptococci, which are part of the normal oral flora. The pathogenesis involves bacterial colonization of previously damaged or abnormal heart valves, leading to the formation of vegetations composed of bacteria, fibrin, and inflammatory cells. This condition primarily affects patients with preexisting valvular abnormalities or prosthetic valves. Clinically, SBE presents with low-grade fever, malaise, and new or changing heart murmurs. The infection can cause valvular destruction, leading to heart failure, systemic emboli, and immune complex-mediated phenomena such as glomerulonephritis. Diagnosis and management are critical to prevent these serious complications.
Inciting Event
Transient bacteremia following dental manipulation or oral trauma
Minor mucosal injuries during dental cleaning or procedures
Spontaneous bacteremia from poor oral hygiene
Invasive procedures involving respiratory or gastrointestinal tracts
Use of intravenous catheters or injections introducing bacteria
Latency Period
Symptoms typically develop over weeks to months after bacteremia
Subacute progression with gradual onset of constitutional symptoms
Latency can range from 2 to 8 weeks post inciting event
Delayed diagnosis common due to indolent symptomatology
Vegetation formation and valvular damage evolve slowly over time
Diagnostic Delay
Nonspecific symptoms such as fatigue and low-grade fever mimic other illnesses
Lack of classic signs like new murmur early in disease course
Misattribution to viral infections or autoimmune diseases
Blood cultures may be initially negative if antibiotics were given
Subtle or absent peripheral stigmata delay clinical suspicion
Clinical Presentation
Signs & Symptoms
Low-grade fever persisting for weeks
Fatigue and malaise due to chronic infection
Night sweats and weight loss reflecting systemic illness
New or worsening heart murmur indicating valvular involvement
Embolic phenomena such as stroke or splenic infarcts causing focal symptoms
History of Present Illness
Gradual onset of low-grade fever, malaise, and night sweats over weeks
New or changing heart murmur indicating valvular involvement
Symptoms of anemia, weight loss, and arthralgias due to chronic inflammation
Possible embolic phenomena causing focal neurological deficits or infarcts
Signs of heart failure in advanced valvular destruction
Past Medical History
History of rheumatic heart disease or congenital valve defects
Previous episodes of infective endocarditis
Recent dental procedures or poor oral hygiene
Presence of prosthetic heart valves or intracardiac devices
Chronic illnesses causing immunosuppression
Family History
No significant familial inheritance pattern for subacute bacterial endocarditis
Family history may reveal heritable valvular disorders increasing risk
Rare familial syndromes with connective tissue abnormalities may predispose
No direct genetic predisposition to infection by viridans streptococci
Family history of congenital heart disease may be relevant
Physical Exam Findings
New or changing heart murmur, often a systolic regurgitant murmur due to valvular damage
Splinter hemorrhages under the fingernails or toenails indicating microvascular emboli
Osler nodes, which are tender, raised lesions on fingers or toes caused by immune complex deposition
Janeway lesions, painless erythematous macules on palms and soles representing septic emboli
Roth spots, retinal hemorrhages with pale centers seen on fundoscopic exam
Diagnostic Workup
Diagnostic Criteria
Diagnosis of subacute bacterial endocarditis relies on the Duke criteria, which include major and minor criteria. Major criteria involve positive blood cultures for typical organisms such as viridans streptococci and evidence of endocardial involvement on echocardiography (e.g., vegetations, abscess, or new valvular regurgitation). Minor criteria include predisposing heart conditions, fever, vascular phenomena, immunologic phenomena, and positive blood cultures not meeting major criteria. Confirmatory diagnosis requires either two major criteria, one major and three minor criteria, or five minor criteria. Repeated blood cultures and transesophageal echocardiography are key to establishing the diagnosis.
Pathophysiology
Key Mechanisms
Bacteremia with seeding of damaged or abnormal heart valves by viridans group streptococci
Formation of vegetations composed of bacteria, fibrin, and platelets on the endocardial surface
Immune complex deposition causing glomerulonephritis and other systemic manifestations
Continuous low-grade infection leading to valvular destruction and potential heart failure
Embolization of vegetations causing systemic infarcts and metastatic infections
| Involvement | Details |
|---|---|
| Organs | Heart is the main organ affected, with vegetations on valves causing valvular insufficiency and heart failure. |
Kidneys may be affected by immune complex deposition leading to glomerulonephritis. | |
Spleen can develop infarcts or abscesses due to septic emboli from vegetations. | |
| Tissues | Endocardium is the primary site of infection and vegetation formation in subacute bacterial endocarditis. |
Valvular tissue undergoes destruction and fibrosis due to bacterial invasion and immune response. | |
| Cells | Neutrophils are the primary immune cells involved in phagocytosis of bacteria in infected heart valves. |
Macrophages contribute to granulomatous inflammation and clearance of bacterial debris in vegetations. | |
Platelets aggregate on damaged endocardium, facilitating vegetation formation. | |
| Chemical Mediators | Interleukin-1 (IL-1) promotes inflammation and fever during infection. |
Tumor necrosis factor-alpha (TNF-α) mediates systemic inflammatory response and tissue damage. | |
C-reactive protein (CRP) is an acute phase reactant elevated in subacute bacterial endocarditis. |
Treatments
Pharmacological Treatments
Penicillin G
- Mechanism:
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, leading to bacterial lysis.
- Side effects:
Hypersensitivity reactions
Nephrotoxicity
Neurotoxicity
- Clinical role:
First-line
Gentamicin
- Mechanism:
Binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting bacterial protein synthesis.
- Side effects:
Nephrotoxicity
Ototoxicity
Neuromuscular blockade
- Clinical role:
Adjunctive
Vancomycin
- Mechanism:
Inhibits bacterial cell wall synthesis by binding to D-Ala-D-Ala terminus of cell wall precursors.
- Side effects:
Nephrotoxicity
Red man syndrome
Ototoxicity
- Clinical role:
Second-line
Non-pharmacological Treatments
Surgical valve repair or replacement is indicated in cases of severe valvular dysfunction, persistent infection, or embolic complications.
Supportive care includes management of heart failure symptoms with diuretics and afterload reduction.
Regular monitoring with echocardiography to assess vegetation size and valvular function.
Prevention
Pharmacological Prevention
Prophylactic antibiotics (e.g., amoxicillin) before dental or invasive procedures in high-risk patients
Long-term suppressive antibiotic therapy in select patients with recurrent endocarditis
Prompt treatment of dental infections to reduce bacteremia risk
Use of appropriate antibiotic regimens targeting viridans group streptococci for eradication
Avoidance of unnecessary invasive procedures without prophylaxis in at-risk individuals
Non-pharmacological Prevention
Good oral hygiene to reduce colonization by viridans streptococci
Regular dental care and screening to prevent dental infections
Avoidance of intravenous drug use which increases endocarditis risk
Careful monitoring and management of pre-existing valvular disease
Education on recognizing early symptoms to prompt timely medical evaluation
Outcome & Complications
Complications
Heart failure due to valvular destruction and regurgitation
Systemic embolization causing stroke, renal infarcts, or splenic abscesses
Perivalvular abscess formation leading to conduction abnormalities
Glomerulonephritis from immune complex deposition
Septic metastases to other organs
| Short-term Sequelae | Long-term Sequelae |
|---|---|
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Differential Diagnoses
Subacute Bacterial Endocarditis (Viridans group streptococci) versus Acute Bacterial Endocarditis (Staphylococcus aureus)
Subacute Bacterial Endocarditis (Viridans group streptococci) | Acute Bacterial Endocarditis (Staphylococcus aureus) |
|---|---|
Indolent, subacute course with low-grade fever and nonspecific symptoms | Rapid onset with severe systemic symptoms and high fever |
Blood cultures positive for viridans group streptococci | Blood cultures positive for Staphylococcus aureus |
Typically follows dental procedures or poor dental hygiene | Often follows intravenous drug use or healthcare-associated procedures |
Subacute Bacterial Endocarditis (Viridans group streptococci) versus Nonbacterial Thrombotic Endocarditis (NBTE)
Subacute Bacterial Endocarditis (Viridans group streptococci) | Nonbacterial Thrombotic Endocarditis (NBTE) |
|---|---|
Vegetations with positive blood cultures for viridans streptococci | Sterile vegetations on echocardiogram with negative blood cultures |
Subacute symptoms with constitutional signs and embolic phenomena | Often associated with advanced malignancy or hypercoagulable states, usually asymptomatic |
Vegetations contain bacteria and inflammatory cells | Vegetations composed mainly of fibrin and platelets without significant inflammation |
Subacute Bacterial Endocarditis (Viridans group streptococci) versus Rheumatic Heart Disease
Subacute Bacterial Endocarditis (Viridans group streptococci) | Rheumatic Heart Disease |
|---|---|
No preceding streptococcal pharyngitis; preceded by dental manipulation or poor oral hygiene | History of untreated or inadequately treated group A streptococcal pharyngitis |
Vegetations composed of bacteria on previously normal or damaged valves | Chronic valvular scarring with Aschoff bodies and leaflet thickening |
Subacute infection with systemic symptoms and embolic events | Chronic progressive valvular dysfunction often years after initial infection |
Subacute Bacterial Endocarditis (Viridans group streptococci) versus Libman-Sacks Endocarditis
Subacute Bacterial Endocarditis (Viridans group streptococci) | Libman-Sacks Endocarditis |
|---|---|
Positive blood cultures for viridans group streptococci with vegetations on valve leaflets | Negative blood cultures with sterile vegetations seen on both sides of valve leaflets |
No autoimmune disease association | Associated with systemic lupus erythematosus and antiphospholipid syndrome |
Subacute systemic illness with fever and embolic phenomena | Usually asymptomatic or mild valvular dysfunction without systemic infection signs |
Subacute Bacterial Endocarditis (Viridans group streptococci) versus Infective Endocarditis due to Enterococci
Subacute Bacterial Endocarditis (Viridans group streptococci) | Infective Endocarditis due to Enterococci |
|---|---|
Blood cultures positive for viridans group streptococci | Blood cultures positive for Enterococcus faecalis or faecium |
Typically follows dental procedures or poor oral hygiene | Often follows genitourinary or gastrointestinal procedures |
Usually treated successfully with penicillin or ceftriaxone monotherapy | Requires combination antibiotic therapy due to intrinsic resistance |