Most common cause of Non gonococcal urethritis is –
**Core Concept**
Non-gonococcal urethritis (NGU) is a sexually transmitted infection characterized by inflammation of the urethra, not caused by *Neisseria gonorrhoeae*. The condition is primarily associated with infections caused by *Chlamydia trachomatis*.
**Why the Correct Answer is Right**
*Chlamydia trachomatis*, specifically serovars L1, L2, and L3, is the most common cause of NGU in sexually active men. The bacteria infect the urethral mucosa, leading to symptoms such as urethral discharge, dysuria, and urinary frequency. The pathogenesis involves the adherence of *Chlamydia trachomatis* to the urethral epithelial cells, followed by the invasion of the host cells, and the subsequent release of the bacteria from the cell.
**Why Each Wrong Option is Incorrect**
**Option A:** *Ureaplasma urealyticum* is another causative agent of NGU, but it is less common than *Chlamydia trachomatis*.
**Option B:** *Trichomonas vaginalis* is a sexually transmitted parasite that can cause urethritis, but it is not the most common cause of NGU.
**Option C:** *Mycoplasma genitalium* has been increasingly recognized as a cause of NGU, but it is still less common than *Chlamydia trachomatis*.
**Clinical Pearl / High-Yield Fact**
It is essential to consider *Chlamydia trachomatis* and *Neisseria gonorrhoeae* as the primary causes of urethritis in sexually active men, and to perform appropriate diagnostic testing to guide treatment.
**Correct Answer: C. *Chlamydia trachomatis***