## Epidemic Keratoconjunctivitis (EKC) — Viral Aetiology **Key Point:** Adenovirus type 8 is the most common cause of EKC worldwide, followed by types 19 and 37. These are highly contagious and spread via contaminated hands, fomites, and ophthalmic instruments. ### Adenovirus Type 8 Characteristics - **Incubation period:** 5–12 days - **Presentation:** Acute follicular conjunctivitis with severe photophobia and foreign body sensation - **Keratitis pattern:** Subepithelial infiltrates (hallmark finding), appearing 1–2 weeks after onset - **Duration:** Self-limiting; typically resolves in 3–4 weeks, but subepithelial infiltrates may persist longer - **Transmission:** Highly contagious; spreads rapidly in healthcare settings and schools ### Comparison with Other Viral Causes | Virus | Keratitis Type | Subepithelial Infiltrates | Recurrence | Chronicity | | --- | --- | --- | --- | --- | | Adenovirus 8 | Epidemic (EKC) | Yes (hallmark) | No | Self-limited | | HSV-1 | Dendritic/amoeboid ulcers | No | Yes (frequent) | Chronic/recurrent | | VZV | Disciform/endotheliitis | Rare | Rare | Usually self-limited | | CMV | Endotheliitis/anterior uveitis | No | Rare | Immunocompromised only | **High-Yield:** EKC caused by adenovirus 8 is a notifiable disease in many countries due to its epidemic potential. Strict hand hygiene and instrument sterilization are critical in ophthalmology clinics. **Clinical Pearl:** Subepithelial infiltrates in adenoviral keratitis may cause significant visual symptoms (glare, halos) and can take weeks to months to fully resolve, even after the acute infection has cleared. 
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