THE CONTEXT
Postoperative infections, animal exposure, fastidious organisms and fungal infections produce distinct associations and diagnostic challenges in infective endocarditis.
Postoperative and coagulase-negative staphylococcal infection
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Endocarditis after cardiac surgery may involve native valves, prosthetic valves or other prosthetic materials.
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The most common postoperative organisms are coagulase-negative staphylococci, such as Staphylococcus epidermidis. These organisms form part of normal skin flora and are often found in wound infections.
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Coagulase-negative staphylococci cause approximately 5% of native valve endocarditis cases and should not automatically be dismissed as blood culture contaminants.
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Staphylococcus lugdunensis can cause rapidly destructive acute endocarditis involving previously normal valves, with multiple emboli. Inaccurate identification may lead to its dismissal as a contaminant.
Endocarditis associated with animal contact
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Q fever endocarditis is caused by Coxiella burnetii and often follows contact with farm animals.
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Q fever endocarditis usually affects the aortic valve and may be accompanied by hepatitis, pneumonia and purpura. Lifelong antibiotic therapy may be required.
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Brucella endocarditis is associated with contact with goats or cattle and often affects the aortic valve.
HACEK organisms
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The HACEK group causes about 3%–4% of endocarditis cases.
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The group includes Aggregatibacter aphrophilus, formerly Haemophilus aphrophilus; Aggregatibacter actinomycetemcomitans; Cardiobacterium hominis; Eikenella corrodens; and Kingella kingae.
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These organisms are slow-growing, fastidious Gram-negative oropharyngeal commensals.
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Diagnosis may require prolonged culture, and the organisms may be resistant to penicillin.
Blood culture–negative and fungal endocarditis
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Blood culture–negative endocarditis may follow previous antibiotic administration or be caused by yeasts and fungi, including Candida and Aspergillus.
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Fungal infection may involve previously normal or prosthetic valves, particularly in immunocompromised patients or those with indwelling intravenous catheters.
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Abscesses and emboli are common in fungal endocarditis. Treatment is difficult, surgery is often required and mortality is high.
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Concomitant bacterial infection may be present.