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.
Viridans streptococci and Enterococci are the second and third most common organisms responsible for infective endocarditis. Viridans streptococci are a common cause of infective endocarditis in South America. Other Streptococci  are also a frequent cause. Infective endocarditis due to Streptococcus bovis occurs more commonly in Europe than in North America. HACEK group of bacteria are also rare causes of infective endocarditis in North America.The viridans group includes S. oralis, S. mitis, S. sanguis, S. gordonii and S. parasanguis. The primary habitats for these organisms are the oral cavity and upper respiratory tract. These bacteria are present in the normal oral flora and enter the bloodstream due to disruption of tissues in the mouth when dental surgical procedures are performed (tooth extractions) or genitourinary manipulation. Similarly, HACEK organisms are a group of bacteria that live on the dental gums and can be seen with people who inject drugs who contaminate their needles with saliva. Patients may also have a history of poor dental hygiene or pre-existing valvular disease.Viridans alpha-hemolytic streptococci, that are present in the mouth, are the most frequently isolated microorganisms when the infection is acquired in a community setting.