A 28-year-old woman presents with a 3-day history of bilateral eye redness, watery discharge, and mild photophobia. She reports recent upper respiratory tract infection. On examination, she has diffuse conjunctival injection, follicular reaction on the tarsal conjunctiva, and preauricular lymphadenopathy. Corneal involvement shows fine punctate epithelial keratitis. What is the most likely causative organism?

Explanation

## Diagnosis: Epidemic Keratoconjunctivitis (EKC) **Key Point:** The clinical triad of follicular conjunctivitis + preauricular lymphadenopathy + punctate epithelial keratitis is pathognomonic for adenoviral keratoconjunctivitis, particularly serotypes 8, 19, and 37. **High-Yield:** Adenovirus causes epidemic keratoconjunctivitis (EKC), which is highly contagious and spreads via direct contact and fomites. The disease is self-limited, lasting 7–14 days for conjunctivitis but keratitis may persist for weeks. ### Clinical Features of Adenoviral Conjunctivitis | Feature | Presentation | |---------|-------------| | **Onset** | Acute, 24–48 hours | | **Discharge** | Watery, scanty | | **Conjunctival reaction** | Diffuse injection with follicles (especially tarsal) | | **Lymphadenopathy** | Preauricular (pathognomonic) | | **Corneal involvement** | Punctate epithelial keratitis (PEK), subepithelial infiltrates | | **Duration** | 7–14 days (keratitis may persist 2–3 months) | | **Systemic signs** | URI prodrome common | **Clinical Pearl:** Preauricular lymphadenopathy is the most discriminating sign that points to viral (especially adenoviral) rather than bacterial conjunctivitis. **Mnemonic: VIRAL CONJUNCTIVITIS — Follicles, Preauricular lymph nodes, Watery discharge, Keratitis** ### Why Adenovirus and Not Other Viruses? - **Herpes simplex:** Would show vesicular lesions, unilateral involvement, and dendritic ulcer on cornea (not PEK) - **Enterovirus 70:** Causes acute hemorrhagic conjunctivitis with subconjunctival hemorrhages (not follicles or keratitis) - **Measles:** Would have Koplik spots and systemic rash **Tip:** The combination of URI prodrome + bilateral follicular conjunctivitis + preauricular lymph node enlargement + PEK is virtually diagnostic of adenoviral EKC without need for viral culture.