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) . 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:
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 .
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 .
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.