One week after having unprotected sexual intercourse, a 25-year-old male develops urethral discharge as shown in the image below. What is the most likely causative organism for this condition? La d

Correct Answer: A. Neisseria gonorrheae

Neisseria gonorrheae is the most common cause of acute bacterial urethritis with purulent urethral discharge in males, presenting within 2–7 days of unprotected sexual contact. The organism is a gram-negative, kidney-bean-shaped diplococcus that preferentially infects the columnar epithelium of the urethra. The acute inflammatory response triggers polymorphonuclear leukocyte infiltration, resulting in the characteristic thick, yellowish-green purulent discharge ("gonorrhea" = flow of seed). In India, gonorrhea remains a leading cause of sexually transmitted urethritis despite declining prevalence in some urban centers. The short incubation period (2–7 days), acute presentation with dysuria and copious discharge, and the epidemiological context of unprotected intercourse all point to N. gonorrheae. Gram stain of urethral exudate showing gram-negative intracellular diplococci within neutrophils is diagnostic. Culture on Thayer-Martin medium (selective for Neisseria) confirms the diagnosis. Untreated infection can ascend to cause epididymitis, prostatitis, and urethral strictures—complications still encountered in Indian clinical practice due to delayed diagnosis or antimicrobial resistance.

Why the other options are wrong

B. Ureplasma urealyticum — Ureaplasma causes non-gonococcal urethritis (NGU), typically presenting 1–3 weeks post-exposure with mucoid or clear discharge rather than purulent discharge. The incubation period is longer, and the discharge is scanty and watery. While Ureaplasma is a common cause of NGU in India, the acute purulent presentation here is classic for gonorrhea, not atypical urethritis. C. Herpes simplex virus — HSV causes vesicular lesions and painful ulcers on the genitalia, not urethral discharge. The presentation includes systemic symptoms (fever, malaise) and painful pustules that rupture into ulcers. While HSV can cause urethritis, the primary lesion is ulcerative, not purulent discharge. The 1-week timeline is consistent, but the discharge character and lesion morphology differ fundamentally. D. Trichomonas vaginalis — Trichomonas is a protozoan that causes urethritis with frothy, greenish discharge predominantly in females; male infection is often asymptomatic or causes mild urethritis. The discharge in trichomoniasis is typically frothy and foul-smelling, not the thick purulent discharge seen here. Incubation is 4–20 days, and the organism is motile on wet mount—a different diagnostic approach than gram stain.

High-Yield Facts

Mnemonics

PURULENT discharge → GONORRHEA (acute) Purulent (thick, yellow-green) = Gonorrhea (2–7 days). Mucoid (clear, scanty) = Non-gonococcal (1–3 weeks). Use this to distinguish acute bacterial urethritis from atypical urethritis at the bedside. GC = Gram-negative Cocci (kidney-bean shape) Neisseria gonorrheae on gram stain: gram-negative, kidney-bean-shaped diplococci inside PMNs. This morphology + intracellular location = pathognomonic for gonorrhea in urethral smear.

NBE Trap

NBE may pair "non-gonococcal urethritis" with Ureaplasma to trap students who conflate all bacterial urethritis. The key discriminator is discharge character and incubation period: purulent + acute (2–7 days) = gonorrhea; mucoid + subacute (1–3 weeks) = NGU.

Clinical Pearl

In Indian STI clinics, the "purulent discharge + 1-week history" triad is so specific for gonorrhea that empiric ceftriaxone + azithromycin is started immediately after gram stain, without awaiting culture—this dual therapy also covers emerging fluoroquinolone-resistant strains and concurrent NGU, reducing treatment failure and complications like strictures.

_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 23 (Neisseria); Harrison's Principles of Internal Medicine Ch. 137 (Sexually Transmitted Infections)_