What Is The Most Common Cause Of Infective Endocarditis?
Endocarditis is a life threatening disease identified as the inflammation of the mural endocardium, which is the innermost layer of the heart. Typically in this disease, cardiac valves are affected, but it may also involve the septum and endocardium structures and often associated with destruction of tissue involved. Infective endocarditis can be classified into Acute Endocarditis and Sub-Acute Endocarditis. In acute form infections are difficult to cure by prescribing antibiotics alone, thus require surgical intervention. While, sub-acute endocarditis is a chronic disease which develops slowly and by severity is less destructive so it can be treated by antibiotics alone.
What is the Most Common Cause Of Infective Endocarditis?
Though development of the disease may be multifactorial, the main pathology behind the disease is formation of vegetations on previously damaged valve as seen in rheumatic heart disease or direct damage to cardiac tissue by a microorganism. This comprises of the thrombotic debris and the causative micro-organisms which usually belong to Staphylococcus and Streptococcus bacterial group, but some strains of Enterococcus have also been registered to cause such infections. In some cases, the infections by fungus have also been registered. Staphylococcus is highly virulent and it produces destructive and necrotizing lesions rapidly.
The causative organisms vary among different high risk groups. Native endocarditis of already damaged or previously abnormal valve have been observed to be caused most commonly (50% to 60%) by Streptococcus viridans, which is a common resident of normal oral cavity. Contrast to this, Staphylococcus aureus which is highly virulent organism and indistinguishably present all over the skin can infect impaired as well as healthy valve thus, accounting for 20% or 30% of the overall cases of infective endocarditis. Surprisingly, there is strong relation observed between intravenous drug abuse and S. aureus infection among different species. There are some other bacteria which can cause this condition belongs to group Enterococcus. A special group has been named as HACEK which is abbreviation for endocarditis causing Enterococci. It refers to H = Haemophilus, A = Actinobacillus, C = Cardiobacterium, E = Eikenella and K = Kingella. All of these organisms are commensals of oral cavity. There are another strains of coagulase negative Staphylococci known to be causing prosthetic endocarditis. For example, S. epidermis is most common causative organisms of the aforementioned condition. Other etiological agents are fungi and gram negative bacteria.
In 10 percent of the overall cases, there is no specific finding of the causative organisms. There are studies providing basis for non-conclusive investigations. According to them, it is antibacterial therapy prior to investigations that hide the infection and make it extremely hard to detect which organism is responsible for the symptoms. In such cases, a medical practitioner has to rely solely on clinical examinations, symptoms and history of the patient and come up with a diagnosis based on the experience.
Factors Predisposing to the Clinical Condition
Foremost factor are those micro-organisms that have ability to seed into the blood circulation resulting bacteremia or fungemia. The sources need not necessarily to be a direct one, but it can be from a much obvious infection somewhere else, or a surgical or dental procedure. It can also be a contaminated needle which is shared by drug abusers commonly. Need not to say, trivial seeming breaks in the endothelial lining of hollow organs like gut, skin or oral cavity may also cause sepsis resulting in profound bacteremia. There are certain other risk factors to be considered while making a diagnosis which are mentioned below -
- Previous history of the endocarditis.
- Artificial or prosthetic valve implantation.
- Congenital heart diseases.
- Complete heart transplant (post-operative cardiac valvulopathy).
- Intravenous drug abuse.
- Valvular stenosis.
- Valvular prolapse.
Though there are multiple other predisposing factors, but scenario can be controlled in high risk individuals by providing them with prophylactic antibiotic therapy.
Though there are numerous pathological agents causing the infective endocarditis. In general, we can say that most common causes of infective endocarditis are Streptococcus viridans and Staphylococcus aureus. Depending on the presentation of the disease, medication or surgical procedure has to be followed.