What is the most common cause of viral conjunctivitis in a healthy adult with a mild upper‑respiratory viral illness?

What Causes Viral Conjunctivitis

Adenovirus is the most common cause of viral conjunctivitis, accounting for approximately 80% of all viral conjunctivitis cases, and in a healthy adult with concurrent upper respiratory infection, adenoviral pharyngoconjunctival fever (PCF) is the most likely diagnosis. 1, 2, 3

Primary Causative Agents

Adenovirus (Most Common)

• Adenovirus causes 80% of all acute viral conjunctivitis cases and is the most frequent infectious conjunctivitis overall 2, 3
• In the context of concurrent upper respiratory infection, adenoviral PCF presents with the classic triad: fever, pharyngitis, and bilateral conjunctivitis 1, 4
• The infection spreads through hand-to-eye contact, ocular secretions, respiratory droplets, and contaminated medical instruments 3
• Epidemic keratoconjunctivitis (EKC) represents the most severe adenoviral form, while PCF is the second most common manifestation 3

Other Viral Causes

• Herpes simplex virus (HSV) typically presents unilaterally with distinctive vesicular eyelid lesions and dendritic corneal ulcers 1
• Varicella zoster virus (VZV) causes unilateral conjunctivitis with painful vesicular dermatomal rash 1
• Enteroviruses represent another common viral cause, though less frequent than adenovirus 2
• Molluscum contagiosum can cause chronic follicular conjunctivitis, particularly in immunocompromised patients 5
• Emerging pathogens including SARS-CoV-2, Zika, Mpox, and arboviruses can manifest with conjunctivitis, typically identified through travel history and exposure patterns 1, 6

Clinical Context: Upper Respiratory Infection

When viral conjunctivitis occurs alongside upper respiratory symptoms, this strongly indicates adenoviral etiology, as bacterial conjunctivitis does not cause concurrent respiratory tract infections 4

The key distinguishing features supporting adenoviral PCF include:

• Bilateral involvement (though may start unilaterally) with watery to serofibrinous discharge 1, 4
• Follicular reaction on inferior tarsal conjunctiva 5, 4
• Preauricular or periauricular lymphadenopathy 1, 4
• Tonsillar exudates as the pharyngeal component 5
• Self-limited course resolving within 5-14 days 1, 4

Critical Diagnostic Pitfall

Always examine the cornea with fluorescein staining in any viral conjunctivitis case to detect early corneal involvement, as progression to EKC can cause subepithelial infiltrates, corneal scarring, and long-term visual sequelae 5, 4

Severe cases developing pseudomembranes carry higher risk of conjunctival/subtarsal scarring, symblepharon, keratitis, dry eye, and lacrimal stenosis 1, 4

Diagnostic Testing

Viral diagnostic tests are not routinely required when clinical presentation is classic (conjunctivitis with upper respiratory infection), as diagnosis can be made on history and examination alone 1, 6

However, rapid immunodiagnostic tests for adenovirus are available with:

• Sensitivity: 88-89% (though some studies show variable sensitivity 40-93%) 1
• Specificity: 91-94% 1
• PCR testing offers higher sensitivity and specificity for definitive diagnosis 1

These tests may prevent misdiagnosis, unnecessary antibiotic use, and disease spread, though they are not mandatory for typical cases 1