A 28 year old sexually active male presents with burning micturation. On clinical examination no ulcer in the genitals. Urine examination shows 50 WBCs/HPF, no RBCs, leucocyte esterase positive, gonococcal culture negative. What could be the most probable causative organism ?

**Core Concept**
Urinary tract infections (UTIs) in sexually active young adults, particularly those without symptoms of urethritis or genital ulcers, can be caused by various pathogens, including bacteria and viruses. The patient's symptoms of burning micturation and the presence of white blood cells (WBCs) in the urine suggest a bacterial or viral etiology.

**Why the Correct Answer is Right**
The patient's symptoms and laboratory results are most consistent with a diagnosis of urethritis caused by Chlamydia trachomatis. Chlamydia is a common sexually transmitted infection that can cause urethritis, particularly in young adults. The presence of 50 WBCs/HPF, positive leucocyte esterase, and negative gonococcal culture supports this diagnosis. Chlamydia trachomatis infects the epithelial cells of the urethra, leading to inflammation and the production of WBCs.

**Why Each Wrong Option is Incorrect**
**Option A:** Neisseria gonorrhoeae is a common cause of urethritis, but the patient's gonococcal culture is negative, making this option less likely.
**Option B:** Escherichia coli is a common cause of lower urinary tract infections, but the patient's symptoms and laboratory results suggest a more acute urethritis, which is less typical for E. coli.
**Option C:** Klebsiella pneumoniae can cause urinary tract infections, but it is less common in young adults and is not typically associated with urethritis.

**Clinical Pearl / High-Yield Fact**
Chlamydia trachomatis is a common cause of urethritis in sexually active young adults, and its diagnosis may require nucleic acid amplification testing (NAAT) or serological testing, as culture is less sensitive.

**Correct Answer:** C. Chlamydia trachomatis.

✓ Correct Answer: C. Chlamydia trachomatis