Which GU infection is associated with reactive arthritis?

• A. Neisseria gonorrhoeae
• B. Chlamydia trachomatis
• C. Treponema pallidum
• D. Listeria monocytogenes

Answer: (B)

Reactive arthritis is a sterile inflammatory arthritis that follows a mucosal infection, most classically a genitourinary infection with Chlamydia trachomatis. After the initial infection may have resolved or been mild, the immune system can drive joint inflammation weeks later, without bacteria in the joint itself. Chlamydia trachomatis is the prototypical GU trigger for this pattern.

The other organisms listed don’t fit this classic linked mechanism. Neisseria gonorrhoeae can cause joint infection during active infection (gonococcal arthritis) but that’s an infectious, bacterial arthritis rather than the reactive, sterile type. Treponema pallidum can cause arthritis in later syphilis, but it isn’t the typical GU-triggered reactive arthritis. Listeria monocytogenes isn’t a recognized GU trigger for reactive arthritis.