Most common organism causing native valve endocarditis in IV drug users?

• A. Streptococcus viridans
• B. Enterococcus faecalis
• C. Pseudomonas aeruginosa
• D. Staphylococcus aureus

Answer: (D)

Staphylococcus aureus is the most common organism causing native-valve endocarditis in people who inject drugs. The practice of injecting drugs can introduce skin bacteria directly into the bloodstream, and S. aureus is highly virulent and adept at seeding heart valves, often presenting acutely. In IV drug users, infection frequently involves the tricuspid valve on the right side of the heart because venous return first reaches the right heart. While Pseudomonas aeruginosa is also seen in this population, it is less common than S. aureus. The viridans group streptococci and Enterococcus faecalis are more typical of endocarditis related to dental disease or GI/GU sources, respectively, and are less tied to IV drug use.