Infective Endocarditis: Diagnosis

Michael Davis

Jonathan P. Moorman

Infective endocarditis refers to the microbial infection of the valvular and nonvalvular endothelium of the heart. Classification of infective endocarditis has been based on clinical presentation, with both acute and subacute forms of disease. The annual incidence of endocarditis is estimated to be 2 to 7 per 100,000. Four components are characteristic: (i) cardiac involvement, (ii) systemic inflammation, (iii) embolic phenomena, and (iv) immune complex disease.

ETIOLOGY AND RISK FACTORS

Native valve endocarditis (NVE) is primarily caused by streptococci and Staphylococcus aureus (>70% of cases), but less common bacterial causes include the HACEK group (Haemophilus, Actinobacillus, Corynebacterium, Eikenella, and Kingella), other gram-negative bacilli, community-acquired enterococci, and Neisseria species. Other organisms include Chlamydia, Mycoplasma, Legionella, Bartonella, Brucella, Tropheryma, Rickettsia, and fungi.
S. aureus is the most common pathogen found in IV drug users, followed by streptococci and enterococci. The tricuspid valve is the most common site. Septic pulmonary emboli are common.
Prosthetic valve endocarditis (PVE) is usually due to Staphylococcus aureus or Staphylococcus epidermidis. Early PVE occurs within 2 months of surgery, late PVE after 2 months.

Pathogen	Frequency (%)
S. aureus	32
Viridans streptococci	18
Enterococcus	11
Coagulase-negative Staphylococcus	11
Streptococcus bovis	7
Streptococcus (other)	5
HACEK	2
Gram-negative bacilli	2
Fungi	2
Culture-negative^a	8
^aMay include Coxiella, Legionella, Mycoplasma, Tropheryma whippelii, Brucella, Bartonella, and Chlamydia.