A 58-year-old man with diabetes mellitus presents with acute onset of severe pain, swelling, and erythema of the right knee with fever of 39.5°C. Synovial fluid analysis shows 80,000 WBC/µL with 95% neutrophils. Gram stain is pending. What is the most common causative organism in adult septic arthritis?
- A Staphylococcus aureus ✓
- B Neisseria gonorrhoeae
- C Streptococcus pneumoniae
- D Escherichia coli
Correct answer: A. Staphylococcus aureus
Explanation
Staphylococcus aureus is the most common cause of septic arthritis in adults overall, including both native and prosthetic joints. Neisseria gonorrhoeae is the most common cause in young sexually active adults, but S. aureus remains the leading cause across all adult age groups. Empiric antibiotics should cover MRSA in many settings.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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