Definition
1. Infective endocarditis (IE) is an infection of the endothelial lining of the valves and heart chambers.
2. Nosocomial IE is defined as health–care-associated infection acquired after at least 48 hours of hospitalization.
3. Non-nosocomial health–care-associated IE is defined as infection associated with health care contact in the outpatient setting.
4. Endocarditis is clinically defined as definite or possible based on modified Duke criteria.

Epidemiology
1. The incidence rate of IE has been stable over time. Modification of risk factors result in the emergence of new population of patients at risk, including injection drug users, elderly patients, patients with intravascular prosthesis, and patients exposed to nosocomial bacteremia during invasive medical interventions.
2. Staphylococci, streptococci, and enterococci are the most frequent organisms isolated in native valve endocarditis.
3. In early prosthetic valve endocarditis, staphylococci, gram-negative bacilli, diphtheroids, and Candida species are the most common etiologic agents identified.
4. Approximately 15% of IE is nosocomial, often caused by staphylococci, enterococci, and gram-negative bacilli.
5. Up to 20% of IE cases are culture negative. Culture-negative endocarditis is most commonly due to prior antimicrobial therapy and rare, fastidious organisms that cannot be cultured using standard laboratory methods.

Clinical Features
1. The diagnosis of IE is challenging because signs and symptoms are nonspecific. Endocarditis in the seriously ill hospitalized patient can be missed because of associated underlying diseases and infection in other sites that could also be possible sources of bacteremia.
2. Embolic complications are seen in 20% to 40% of patients and most commonly involve the brain, heart, kidney, spleen, and skin.
3. Immune-complex related phenomena are now rarely seen in IE patients, probably because of earlier diagnosis.
4. Right-sided endocarditis presents with fever, bacteremia, and multiple pulmonary emboli.

Radiologic Features
1. Echocardiography is a sensitive tool to localize vegetations, assess valvular damage, detect perivalvular abscesses and shunts, and evaluate cardiac hemodynamic status.
2. Transesophageal echocardiography is recommended for the investigation of suspected prosthetic valve endocarditis and assessment of perivalvular abscess formation.

Prognosis and Therapy
1. Empiric antimicrobial therapy is started based on the most likely organisms after risk factor assessment.
2. Appropriate antimicrobial therapy guided by susceptibility testing requires long-term parenteral administration.
3. About a third of patients will require surgical intervention. Usual indications for surgery are congestive heart failure, persistent bacteremia, recurrent embolization, and prosthetic valve endocarditis.
4. Mortality is most often due to cardiac complications. Survivors are at risk of recurrent infection.