Subacute Infective Endocarditis: Common Pathogens and Risk Factors

Subacute infective endocarditis (SIE) is a serious infection that affects the inner lining of the heart chambers and valves. One of the most frequently identified causative agents is Streptococcus viridans, also known as viridans group streptococci (VGS). These bacteria are commonly found in the oral cavity and can easily enter the bloodstream during dental procedures or even routine oral hygiene practices.

Why Streptococcus viridans?

Streptococcus viridans has a high affinity for damaged heart tissue, especially abnormal or prosthetic heart valves. Its strong adhesive properties allow it to colonize the endocardium, forming vegetations that can lead to severe complications. In contrast, although Escherichia coli is a common cause of bacteremia, it lacks the same level of adhesion to heart valves and is therefore rarely associated with endocarditis.

Other Common Pathogens

Besides Streptococcus viridans, other bacterial species are also implicated in subacute cases. Group D streptococci, including Streptococcus bovis and Enterococcus species, are notable contributors. Additionally, Staphylococcus epidermidis, a coagulase-negative staphylococcus, is increasingly recognized as a cause, particularly in patients with prosthetic valves or those undergoing long-term invasive medical treatments.

Less Common Microorganisms

While bacterial infections dominate the landscape of infective endocarditis, other microorganisms such as fungi, rickettsiae, and chlamydiae can also be responsible. These are considered rare causes and typically affect immunocompromised individuals or those with prolonged exposure to healthcare settings.

Risk Factors and Patient Profile

Subacute infective endocarditis predominantly occurs in individuals with pre-existing structural heart disease. Patients with conditions such as rheumatic heart disease, congenital heart defects, or degenerative valve disease are at significantly higher risk. The presence of damaged or artificial heart valves provides an ideal surface for microbial attachment and biofilm formation, making infection more likely and harder to treat.