## Epidemic Keratoconjunctivitis (EKC) — Viral Etiology **Key Point:** Adenovirus type 8 (Ad-8) is the most common cause of EKC globally, accounting for >90% of cases in outbreak settings. Ad-3, Ad-7, and Ad-19 are less frequent but still significant. ### Clinical Features of Ad-8 EKC - **Onset:** Acute, highly contagious - **Incubation period:** 5–12 days - **Conjunctival findings:** Follicular response, pseudomembrane, subconjunctival hemorrhages - **Keratitis pattern:** Subepithelial infiltrates (SEI) in the central cornea — pathognomonic - **Systemic:** Preauricular lymphadenopathy (often unilateral initially, then bilateral) ### Differential Viral Keratitis | Virus | Keratitis Type | Hallmark Feature | Recurrence | |-------|---|---|---| | **Ad-8** | Subepithelial infiltrates | EKC, pseudomembrane | Rare; self-limited | | **HSV-1** | Dendritic ulcer (primary), stromal (recurrent) | Branching ulcer with terminal bulbs | Common (latent in trigeminal ganglion) | | **VZV** | Pseudodendritic, stromal | Vesicular rash on lid/forehead (dermatomal) | Rare; post-herpetic neuralgia | | **CMV** | Hemorrhagic, endotheliitis | Immunocompromised hosts (AIDS) | Chronic in immunosuppressed | **High-Yield:** EKC caused by Ad-8 is a **clinical diagnosis** — no specific antiviral is effective. Management is supportive (lubricants, topical NSAIDs for pain, cool compresses). Subepithelial infiltrates may persist for weeks to months but resolve without scarring. **Clinical Pearl:** Preauricular lymphadenopathy is a key sign pointing toward adenoviral EKC rather than HSV keratitis (which rarely causes prominent lymphadenopathy). **Warning:** Do not confuse EKC (adenovirus) with herpetic keratitis — the latter has dendritic ulcers and responds to antivirals (acyclovir); EKC does not respond to antivirals and is managed supportively. 
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