A 28-year-old woman presents with acute onset of bilateral conjunctival injection, chemosis, and copious purulent discharge for 3 days. She reports severe ocular pain and photophobia. On examination, preauricular lymphadenopathy is absent. Gram stain of the discharge shows gram-negative diplococci. What is the most appropriate confirmatory investigation?

Explanation

## Diagnosis: Gonococcal Conjunctivitis **Key Point:** Gram stain showing gram-negative diplococci in a patient with acute purulent conjunctivitis and absence of preauricular lymphadenopathy is highly suggestive of *Neisseria gonorrhoeae* infection. ### Why Culture on Thayer-Martin Medium is Correct **High-Yield:** Thayer-Martin medium is a selective enriched medium containing antibiotics (vancomycin, colistin, nystatin, trimethoprim) that suppress normal flora while allowing *Neisseria gonorrhoeae* to grow. This is the gold standard confirmatory test for gonococcal conjunctivitis [cite:Khurana Textbook of Ophthalmology Ch 5]. **Clinical Pearl:** Gonococcal conjunctivitis is a medical emergency requiring immediate systemic and topical antibiotics. Culture confirmation is essential before initiating treatment, as it also allows antimicrobial susceptibility testing. ### Key Features of Gonococcal vs. Other Bacterial Conjunctivitis | Feature | Gonococcal | Chlamydial | Pneumococcal | |---------|-----------|-----------|---------------| | **Onset** | Acute (1–3 days) | Subacute (5–14 days) | Acute | | **Discharge** | Copious, purulent | Mucopurulent | Purulent | | **Preauricular nodes** | Absent | Present | Absent/mild | | **Gram stain** | Gram-negative diplococci | Intracellular (Giemsa) | Gram-positive cocci | | **Confirmatory test** | Culture on Thayer-Martin | PCR or cell culture | Culture on blood agar | **Mnemonic:** **GC = Gram-negative, Copious discharge, Culture on Thayer-Martin** — remember the three C's for gonococcal conjunctivitis. ### Pathophysiology Gonococcal conjunctivitis occurs when *N. gonorrhoeae* directly infects the conjunctiva, causing acute purulent inflammation. The organism produces pili and lipopolysaccharides that evade innate immunity, leading to severe inflammation without systemic symptoms in early stages.