What is the most common cause of native valve infective endocarditis in the community?

Most Common Cause of Native Valve Infective Endocarditis in the Community

Streptococci are the most common cause of native valve infective endocarditis in the community setting. While the epidemiology of infective endocarditis (IE) has evolved over time, guidelines consistently identify streptococci, particularly viridans group streptococci, as the predominant pathogens in community-acquired native valve endocarditis.

Microbiology of Native Valve Endocarditis

Streptococci

• Viridans group streptococci (VGS) are the most frequently isolated organisms in patients with IE caused by underlying congenital heart disease 1
• After the first year of life, VGS are generally the most frequently isolated organisms in community-acquired native valve IE 1
• Streptococci (viridans) are the predominant pathogens in late-onset prosthetic valve endocarditis, which follows the profile of native valve endocarditis 1

Staphylococci

• Staphylococcus aureus is the second most common cause of IE in many series, though it has become the most common agent in some specific populations 1
• S. aureus is definitely the most common agent of acute (rapidly progressive) bacterial endocarditis 1
• S. aureus is particularly common in:
  • Intravenous drug users (IDUs)
  • Healthcare-associated infections
  • Prosthetic valve endocarditis within the first year after surgery 1

Other Organisms

• Enterococci account for a smaller percentage of cases but are associated with genitourinary or gastrointestinal tract manipulation 1
• Coagulase-negative staphylococci are predominantly associated with prosthetic valve endocarditis but can occasionally cause native valve IE 1
• HACEK group organisms (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella species) are relatively uncommon causes 1

Changing Epidemiology

It's important to note that the epidemiology of IE has been evolving:

• The average age of patients with IE has increased, with a peak incidence in patients between 70-80 years 2
• There has been a decrease in rheumatic heart disease as a predisposing factor in developed countries 2
• The proportion of cases without predisposing heart disease has increased significantly over time 3
• In some healthcare settings and specific populations, S. aureus has become more prevalent 3

Clinical Implications

Understanding the most likely causative organisms has important implications for empiric antibiotic therapy:

• For community-acquired native valve IE, coverage for streptococci should be prioritized
• For healthcare-associated IE or in IDUs, coverage for staphylococci becomes more important
• Empiric therapy should be adjusted based on local antimicrobial resistance patterns

Common Pitfalls to Avoid

• Failing to distinguish between community-acquired versus healthcare-associated IE, which have different microbial profiles
• Not recognizing that prosthetic valve IE has a different microbiology than native valve IE
• Overlooking the possibility of culture-negative endocarditis, which accounts for 5-36% of cases 1
• Not adjusting empiric therapy based on patient risk factors and clinical presentation

In summary, while the epidemiology of IE continues to evolve, streptococci remain the most common cause of community-acquired native valve endocarditis, with S. aureus being the second most common pathogen but predominating in specific clinical scenarios such as healthcare-associated infections and intravenous drug use.