Infective endocarditis, the majority of cases are caused by which type of organisms?

• A. Gram-positive cocci are the majority
• B. Gram-negative rods are the majority
• C. Fungi are the majority
• D. Viruses are the majority

Answer: (A)

Most infective endocarditis cases are caused by Gram-positive cocci. Staphylococcus species, especially Staphylococcus aureus, are the leading cause in acute presentations and in many healthcare-associated infections affecting both native and prosthetic valves. Viridans group streptococci are classic culprits in subacute native valve endocarditis, often after dental procedures. These organisms are part of skin and oral flora and have a strong ability to adhere to damaged or prosthetic valves and form biofilms, fueling infection. Gram-negative rods, fungi, and viruses occur far less frequently and are usually tied to specific situations such as healthcare-associated infections, immunosuppression, or prosthetic devices, but they do not represent the majority.