This was previously a minor criterionEvidence of endocardial involvement with positive echocardiogram is defined as

Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternative anatomic explanation, or
Abscess, or
New partial dehiscence of prosthetic valve or new valvular regurgitation (worsening or changing of preexisting murmur not sufficient)

Minor criteria
Predisposing factor: known cardiac lesion, recreational drug injection
Fever >38 °C
Vascular phenomena: arterial emboli, pulmonary infarcts, Janeway lesions, conjunctival hemorrhage
Immunological phenomena: glomerulonephritis, Oslers nodes, Roths spots, Rheumatoid factor
Microbiologic evidence: Positive blood culture (that doesnt meet a major criterion) or serologic evidence of infection with organism consistent with IE but not satisfying major criterion

Risk
Among people who do not use intravenous drugs and have a fever in the emergency department, there is a less than 5% chance of occult endocarditis. Mellors in 1987 found no cases of endocarditis nor of staphylococcal bacteremia among 135 febrile patients in the emergency room. The upper confidence interval for 0% of 135 is 5%, so for statistical reasons alone, there is up to a 5% chance of endocarditis among these patients. In contrast, Leibovici found that among 113 non-selected adults admitted to the hospital because of fever there were two cases (1.8% with 95%CI: 0% to 7%) of endocarditis.Among people who do use intravenous drugs and have a fever in the emergency department, there is about a 10% to 15% prevalence of endocarditis. This estimate is not substantially changed by whether the doctor believes the patient has a trivial explanation for their fever.
This combination of damaged valves, bacterial growth, and lack of a strong immune response results in infective endocarditis.Damage to the valves and endocardium can be caused by:
Altered, turbulent blood flow. The areas that fibrose, clot, or roughen as a result of this altered flow are known as jet lesions. Altered blood flow is more likely in high pressure areas, so ventricular septal defects or patent ductus arteriosus can create more susceptibility than atrial septal defects. Catheters, electrodes, and other intracardiac prosthetic devices. Solid particles from repeated intravenous injections. Chronic inflammation. Examples include auto-immune mechanisms and degenerative valvular lesions.The risk factors for infective endocarditis provide a more extensive list of conditions that can damage the heart. Diagnosis
In general, the Duke criteria should be fulfilled in order to establish the diagnosis of endocarditis. Although the Duke criteria are widely used, they have significant limitations. For example, the sensitivity of the Duke criteria for detecting infective endocarditis decreases when prosthetic heart valves are present.As the Duke criteria rely heavily on the results of echocardiography, research has addressed when to order an echocardiogram by using signs and symptoms to predict occult endocarditis among people who inject drugs and among non drug-abusing patients. However, this research is over twenty years old and it is possible that changes in the epidemiology of endocarditis and bacteria such as staphylococci make the following estimates incorrect. The blood tests C reactive protein (CRP) and procalcitonin have not been found to be particularly useful in helping make or rule out the diagnosis.