Question 6#

A 45-year-old woman with long-standing, well-controlled rheumatoid arthritis develops severe pain and swelling in the left elbow over 2 days. She is not sexually active. Arthrocentesis reveals cloudy fluid. Synovial fluid analysis reveals greater than 100,000 cells/mL; 98% of these are PMNs. What is the most likely organism to cause this scenario?

A) Streptococcus pneumoniae
B) Neisseria gonorrhoeae
C) Escherichia coli
D) Staphylococcus aureus
E) Pseudomonas aeruginosa

Correct Answer is D


Staphylococcus aureus is the most common organism to cause septic arthritis in adults. β-Hemolytic streptococci are the second most common. N gonorrhoeae can also produce septic arthritis, but would be less likely in this patient who is not sexually active. S pneumoniae and gramnegative rods such as E coli or P aeruginosa are rare causes of septic arthritis and usually occur secondary to a primary focus of infection. Septic arthritis commonly occurs in joints that are anatomically damaged, as in this case with prior rheumatoid arthritis. Any time a patient with arthritis develops a monoarticular flare out of proportion to the other joints, septic arthritis must be suspected.