Which virus is the most common cause of epidemic keratoconjunctivitis (EKC)?

Question

Accepted Answer

A. Adenovirus type 8. ## 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.

![Viral Keratitis diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3900.webp)

Answer

B. Cytomegalovirus

Answer

C. Varicella-zoster virus

Answer

D. Herpes simplex virus type 1

Which virus is the most common cause of epidemic keratoconjunctivitis (EKC)?

Explanation

Epidemic Keratoconjunctivitis (EKC) — Viral Aetiology

Adenovirus Type 8 Characteristics

Comparison with Other Viral Causes

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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