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
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.