A 28-year-old woman presents with acute onset bilateral conjunctivitis, copious purulent discharge, and severe chemosis. She reports recent unprotected sexual contact. On examination, the discharge is thick and creamy. What is the investigation of choice to confirm the diagnosis?

Explanation

## Diagnosis: Gonococcal Conjunctivitis **Key Point:** Neisseria gonorrhoeae causes acute purulent conjunctivitis with copious discharge and severe chemosis, typically following sexual exposure. The organism is fastidious and requires selective media for isolation. **High-Yield:** Gram stain shows gram-negative intracellular diplococci within polymorphonuclear leukocytes (PMNs). Culture on Thayer-Martin medium (selective medium containing antibiotics to suppress normal flora) is the gold standard confirmatory test and allows antibiotic susceptibility testing. ### Investigation Algorithm for Acute Purulent Conjunctivitis ```mermaid flowchart TD A[Acute purulent conjunctivitis]:::outcome --> B{Sexual history?}:::decision B -->|Yes, recent exposure| C[Suspect gonococcal]:::outcome B -->|No clear history| D[Suspect other bacteria]:::outcome C --> E[Gram stain + Culture on Thayer-Martin]:::action D --> F[Gram stain + Culture on blood agar]:::action E --> G[Confirm N. gonorrhoeae]:::outcome F --> H[Identify organism]:::outcome ``` **Clinical Pearl:** Gonococcal conjunctivitis is a medical emergency in neonates (ophthalmia neonatorum) and requires systemic antibiotics in addition to topical therapy. Adult gonococcal conjunctivitis also warrants systemic treatment (ceftriaxone) to prevent disseminated infection. ### Why Gram Stain + Culture on Thayer-Martin? | Feature | Importance | |---------|------------| | Gram stain | Rapid presumptive diagnosis; shows gram-negative diplococci in PMNs | | Thayer-Martin medium | Selective (contains antibiotics); enriched for N. gonorrhoeae | | Culture | Gold standard; allows organism identification and susceptibility testing | | Sensitivity | ~95% for gonococcal conjunctivitis | [cite:Park 26e Ch 7]