A 30-year-old male presents with urethral discharge and dysuria for 5 days. NAAT on urethral swab is positive for Chlamydia trachomatis serovars D–K. Three weeks later he develops sterile arthritis, conjunctivitis, and oral ulcers. What is this clinical triad called, and which is the MOST common causative organism in the current era?

• A Gonococcal arthritis — Neisseria gonorrhoeae disseminated infection
• B Behcet's disease — HLA-B51 associated, not triggered by Chlamydia
• C Ankylosing spondylitis — HLA-B27 associated chronic axial spondyloarthropathy
• D Reactive arthritis (formerly Reiter's syndrome) — C. trachomatis is the most common trigger for post-infectious reactive arthritis in sexually active young males in developed countries ✓

Explanation

Reactive arthritis (ReA, formerly Reiter's syndrome) is the classic triad of seronegative arthritis + urethritis/cervicitis + conjunctivitis/uveitis occurring 2–6 weeks after urogenital or gastrointestinal infection. C. trachomatis (serovars D–K causing urogenital chlamydia) is the most common trigger for sexually acquired reactive arthritis (SARA), particularly in HLA-B27-positive individuals who have higher risk. It is a sterile arthritis — synovial fluid culture is negative. Chlamydial 16S rRNA/DNA can sometimes be detected in synovial fluid by PCR. Gonococcal arthritis is septic (positive joint culture/NAAT).

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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