Subacute Infective Endocarditis: Common Pathogens and Their Pathways

Subacute infective endocarditis (SIE) is a serious infection that primarily affects the heart valves. One of the most frequently identified causative agents is Viridans group streptococci, which accounts for approximately 80% of cases. These bacteria are part of the normal flora found in the oropharynx and typically gain access to the bloodstream through minor trauma such as aggressive tooth brushing, dental procedures, or especially tooth extraction.

Other Bacterial and Fungal Causes of Endocarditis

In addition to Viridans streptococci, Enterococcus species, particularly Streptococcus faecalis, are also known to cause severe forms of endocarditis. These bacteria are commonly found in the gastrointestinal and genitourinary tracts and may enter the bloodstream following procedures such as urinary catheterization, endoscopic examinations, or childbirth, leading to systemic infection and subsequent heart valve involvement.

Fungal Infections and Their Role in Endocarditis

Fungal pathogens, including species of Candida and Histoplasma, have also been implicated in cases of endocarditis. Candida infections are more frequently observed in individuals with compromised immune systems, such as those with diabetes, patients who have undergone cardiac valve replacement, or intravenous drug users. These populations are particularly vulnerable due to repeated exposure to invasive procedures or weakened host defenses.

Less Common but Clinically Significant Pathogens

While anaerobic bacteria are not typically the primary cause of endocarditis, they can play a role in specific circumstances. For example, in the presence of large vegetations on heart valves, areas of poor perfusion may allow anaerobes to establish an infection. This scenario is more likely in patients with pre-existing valvular disease or those who have had prolonged bacteremia.

Other less common pathogens associated with subacute endocarditis include Staphylococcus aureus, Staphylococcus albus (now known as Staphylococcus epidermidis), Rickettsiae, and Enterobacter species. Although these organisms are less frequently implicated, they can still lead to significant morbidity and mortality, especially in immunocompromised individuals or those with prosthetic heart valves.