An elderly patient with a hot, swollen knee aspirated; which bacterial organism is most likely septic arthritis?

An elderly patient with a hot, swollen knee aspirated; which bacterial organism is most likely septic arthritis?

• A. Haemophilus influenzae
• B. Neisseria gonorrhoeae
• C. Pseudomonas aeruginosa
• D. Staphylococcus aureus

Answer: (D)

In adults, septic arthritis is most commonly caused by Staphylococcus aureus, especially in the elderly. This organism frequently colonizes the skin and can spread hematogenously or seed a joint after minor trauma, leading to an acutely hot, swollen knee with pain and limited movement. S. aureus is the leading cause of native joint septic arthritis, which is why it’s the best fit for this presentation. Haemophilus influenzae is more typical in children (or adults with specific vulnerabilities) and is less common in elderly patients. Neisseria gonorrhoeae usually presents in sexually active young adults and often causes migratory polyarthralgia or a purulent arthritis with multiple joints rather than a single native knee in an older individual. Pseudomonas aeruginosa is more associated with hospital-acquired infections, wounds, prosthetic joints, or IV drug use, and while it can cause septic arthritis in those contexts, it’s not the most likely cause in this typical elderly native knee scenario.

In adults, septic arthritis is most commonly caused by Staphylococcus aureus, especially in the elderly. This organism frequently colonizes the skin and can spread hematogenously or seed a joint after minor trauma, leading to an acutely hot, swollen knee with pain and limited movement. S. aureus is the leading cause of native joint septic arthritis, which is why it’s the best fit for this presentation.

Haemophilus influenzae is more typical in children (or adults with specific vulnerabilities) and is less common in elderly patients. Neisseria gonorrhoeae usually presents in sexually active young adults and often causes migratory polyarthralgia or a purulent arthritis with multiple joints rather than a single native knee in an older individual. Pseudomonas aeruginosa is more associated with hospital-acquired infections, wounds, prosthetic joints, or IV drug use, and while it can cause septic arthritis in those contexts, it’s not the most likely cause in this typical elderly native knee scenario.