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.
Infective endocarditis is an infection of the inner surface of the heart, usually the valves. Signs and symptoms may include fever, small areas of bleeding into the skin, heart murmur, feeling tired, and low red blood cell count. Complications may include backward blood flow in the heart, heart failure – the heart struggling to pump a sufficient amount of blood to meet the bodys needs, abnormal electrical conduction in the heart, stroke, and kidney failure.The cause is typically a bacterial infection and less commonly a fungal infection. Risk factors include valvular heart disease, including rheumatic disease, congenital heart disease, artificial valves, hemodialysis, intravenous drug use, and electronic pacemakers. The bacteria most commonly involved are streptococci or staphylococci. Diagnosis is suspected based on symptoms and supported by blood cultures or ultrasound of the heart. There is also a noninfective form of endocarditis.The usefulness of antibiotics following dental procedures for prevention is unclear. Some recommend them for people at high risk. Treatment is generally with intravenous antibiotics. The choice of antibiotics is based on the results of blood cultures. Occasionally heart surgery is required.The number of people affected is about 5 per 100,000 per year. Rates, however, vary between regions of the world. Infective endocarditis occurs in males more often than in females. The risk of death among those infected is about 25%. Without treatment, it is almost universally fatal. Classification
Infective endocarditis is divided into the three categories of acute, subacute, and chronic based on the duration of symptoms.