Subacute Infective Endocarditis: Common Pathogens and Treatment Approaches

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 of SIE is Streptococcus viridans, also known as viridans group streptococci. This is in contrast to acute infective endocarditis, where Staphylococcus aureus is most commonly responsible. The virulence and invasiveness of Streptococcus viridans are generally lower compared to Staphylococcus aureus, which explains why the onset of SIE tends to be more gradual and less aggressive than its acute counterpart.

Clinical Presentation and Disease Progression

Patients with subacute infective endocarditis often present with non-specific symptoms such as fatigue, weight loss, and a persistent low to moderate-grade fever. This is significantly different from acute infective endocarditis, which typically presents with high fever and rapid clinical deterioration. Due to its subtle and progressive nature, SIE can be more challenging to diagnose in its early stages, often leading to delayed treatment.

Complications Associated with Streptococcus viridans

The vegetations formed during subacute endocarditis are predominantly composed of fibrin and bacteria, with Streptococcus viridans being the dominant pathogen. These vegetations can break off and travel through the bloodstream, leading to embolic events. Once these infected fragments reach vital organs such as the liver or spleen, they can cause localized abscesses—most notably, hepatic or splenic abscesses. These complications can significantly increase morbidity and mortality if not promptly diagnosed and treated.

Antibiotic Therapy and Empirical Treatment

Because blood culture results may take several days to become available, empirical antibiotic therapy is often initiated based on the most likely causative organisms. In the case of suspected subacute infective endocarditis, initial treatment typically targets Streptococcus viridans. Commonly used antibiotics include penicillin-based agents, often in combination with aminoglycosides, to provide broad-spectrum coverage and enhance bacterial eradication.

In conclusion, understanding the microbial etiology of subacute infective endocarditis is crucial for guiding appropriate diagnostic and therapeutic strategies. Early recognition of symptoms, prompt initiation of targeted antibiotic therapy, and close monitoring for embolic complications are essential components of effective patient management.