Subacute Bacterial Endocarditis

Although subacute bacterial endocarditis (SBE) develops insidiously and has a slow progression over weeks to months, it is often aggressive. Usually, no evident portal of entry or source of infection can be found. The most common causative microorganism is streptococci (especially viridans, anaerobic, enterococci, microaerophilic, and non-enterococcal group D streptococci). SBE is less commonly caused by staphylococcus epidermidis and staphylococcus aureus. SBE is generally developed on abnormal valves after asymptomatic bacteremia resulting from gastrointestinal, genitourinary, or periodontal infections.

The initial symptoms are vague, including night sweats, malaise, fatigability, weight loss, anorexia, myalgia, dyspnea, and low-grade fever (< 39°C) [1]. Arthralgias and chills are possible. Valvular insufficiency features may be the first clue. Early in the course of the disease, ≤ 15% of patients have a murmur or fever but all eventually develop both. On physical examination, normal findings can be observed or fever, pallor, tachycardia, and change in a murmur or a new regurgitant type may be detected.

Approximately 35% of cases show CNS effects like transient ischemic attacks, stroke, or brain abscesses and subarachnoid hemorrhage due to mycotic aneurysm rupture. Potential renal emboli can result in flank pain. Splenomegaly and clubbing of fingers and toes may occur because of prolonged infection.

The four peripheral signs of endocarditis include:

• Roth spots: Retinal emboli that appear as oval or round hemorrhagic lesions on the retina with white centers on fundoscopic examination. Roth spots are also found in hypertension, vasculitis, diabetes mellitus, and intracranial hemorrhages [2]. Other ocular manifestations are retinal hemorrhages and infectious vitritis in embolic disease [3].
• Osler nodes: Painful subcutaneous and erythematous nodules on the digits tips. Osler nodes are one of the classic signs in late-phase SBE. However, they can be found in other conditions such as bacteremia, systemic lupus erythematosus, and disseminated gonococcal infection. Adequate intravenous antibiotics can resolve Osler nodes within 3 days [4].
• Janeway lesions: Small, erythematous, non-tender, or hemorrhagic macular lesions. They do not have an immunological origin and are present on the palms and soles [5].
• Splinter hemorrhages: Small vertical blood clots under nails. They can also be observed in scleroderma, systemic lupus erythematosus, rheumatoid arthritis, and trauma [6].

The diagnosis of endocarditis is challenging since the presentation varies from case to case. The symptoms of SBE can take several weeks or months to develop while some patients show symptoms acutely after a few days [7].

Laboratory studies may show anemia, leukocytosis, elevated erythrocyte sedimentation rate (ESR), and microscopic hematuria. Although, bacterial endocarditis can be present in the absence of these findings [8].

If endocarditis is suspected, three sets of blood cultures (20 mL each) must be obtained from a separate new venipuncture site within 24 hours.

Echocardiography should be performed. Transthoracic echocardiography (TTE) is usually preferred since it is less costly and non-invasive compared to transesophageal echocardiography (TEE).

The definite diagnosis of infective endocarditis is done when microorganisms are cultured or observed histologically after being obtained from endocardial vegetations during embolectomy, cardiac surgery, or autopsy. Since this is not always possible, diagnostic criteria called revised Duke's criteria has been established with a specificity and sensitivity of more than 90%.

For a definite clinical diagnosis: 2 major criteria are needed, or 1 major and 3 minor criteria, or 5 minor criteria.
For a potential clinical diagnosis: 1 major criterion and 1 minor criterion are needed, or 3 minor criteria.

Major criteria

1. 2 positive blood cultures for typical microorganisms causing endocarditis
2. 3 positive blood cultures for microorganisms that are consistent with endocarditis
3. Serologic evidence of Coxiella burnetii infection (or 1 positive blood culture)
4. Evidence of endocardial involvement on echocardiography:

• Oscillating intracardiac vegetative mass on a valve, or on the supporting structures, in the path of regurgitant jets, or on implanted material without other anatomic explanation
• Cardiac abscess
• Newly developed dehiscence of a prosthetic valve
• New valvular regurgitation

Minor criteria

1. Predisposing cardiac disease
2. Intravenous drug abuse
3. Fever ≥38° C
4. Vascular phenomena: arterial embolism, pulmonary septic embolism, mycotic aneurysm, intracranial hemorrhage, petechiae on the conjunctiva, Janeway lesions
5. Immunologic phenomena: glomerulonephritis, Osler nodes, Roth spots, positive rheumatoid factor
6. Microbiological evidence of infection that is consistent with but not meeting major criteria
7. Serologic evidence of infection with organisms consistent with causing endocarditis

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2. Fred HL. Little black bags, ophthalmoscopy, and the Roth spot. Tex Heart Inst J. 2013;40:115–6.
3. Habib G, Hoen B, Tornos P, et al. Guidelines on the prevention, diagnosis, and treatment of infective endocarditis (new version 2009): The task force on the prevention, diagnosis, and treatment of Infective Endocarditis of the European society of Cardiology (ESC). Eur Heart J. 2009;30(19):2369-413.
4. Jackson TL, Eykyn SJ, Graham EM, Stanford MR. Endogenous bacterial endophthalmitis: a 17-year prospective series and review of 267 reported cases. Surv Ophthalmol. 2003;48:403–23. doi: 10.1016/S0039-6257(03)00054-7.
5. Farrior JB, Silverman ME. A consideration of the differences between a Janeway’s lesion and an Osler’s node in infectious endocarditis. Chest. 1976;70:239–43. doi: 10.1378/chest.70.2.239.
6. Robertson JC, Braune ML. Splinter haemorrhages, pitting, and other findings in fingernails of healthy adults. Br Med J. 1974;4:279–81. doi: 10.1136/bmj.4.5939.279.
7. Luttenberger K, DiNapoli M. Subacute bacterial Endocarditis. J.Nurse Pract. 2011;36(3):31–38. doi:10.1097/01.npr.0000393971.15598.0c.
8. Cunha BA, Gill MV, Lazar JM. Acute infective endocarditis. Diagnostic and therapeutic approach. Infect Dis Clin North Am. 1996;10:811–34.