What is the differential diagnosis for viral conjunctivitis?

Differential Diagnosis of Viral Conjunctivitis

When evaluating a patient with suspected viral conjunctivitis, the key differential diagnoses include bacterial conjunctivitis (particularly hyperacute gonococcal), other viral causes (HSV, VZV, molluscum contagiosum), chlamydial conjunctivitis, allergic conjunctivitis, and non-infectious causes such as dry eye and blepharitis. 1

Primary Infectious Differentials

Bacterial Conjunctivitis

• Nongonococcal bacterial: Presents with purulent or mucopurulent discharge (versus watery in viral), often with eyelids matted shut upon awakening 1, 2
• Hyperacute gonococcal: The most critical to identify—presents with copious purulent discharge, marked eyelid edema, preauricular lymphadenopathy, and risk of superior corneal infiltrates that can perforate within 24 hours 3
• Bacterial conjunctivitis is more common in children, while viral is more common in adults 2
• Critical pitfall: No single sign accurately differentiates viral from bacterial conjunctivitis, but purulent discharge strongly suggests bacterial etiology 2, 4

Other Viral Causes

• HSV conjunctivitis: Usually unilateral with mild follicular reaction, may have vesicular lesions on eyelids or dendritic corneal lesions; subsides in 4-7 days unless complications occur 1
• Varicella-zoster virus (VZV): Distinctive vesicular dermatomal rash or ulceration of eyelids, pleomorphic pseudodendritic epithelial keratitis; typically subsides in a few days 1
• Molluscum contagiosum: Shiny, dome-shaped umbilicated lesion(s) on eyelid skin or margin with associated follicular conjunctivitis; more common in immunocompromised patients 1

Chlamydial Conjunctivitis

• Inclusion conjunctivitis: Caused by Chlamydia trachomatis serotypes D-K; presents with follicular conjunctivitis, chemosis, and mucoid discharge 1
• In neonates, manifests 5-19 days following birth (later than gonococcal at 1-7 days) 1, 5
• In adults, associated with concurrent genitourinary symptoms (cervicitis, urethritis) 1

Non-Infectious Differentials

Allergic Conjunctivitis

• Bilateral presentation with eyelid edema, chemosis, watery discharge, and papillary (not follicular) palpebral reaction 1
• Key distinguishing feature: Itching is a strong indicator of allergic etiology 6, 2
• Associated with environmental allergens, seasonal patterns, and personal/family history of atopy 1

Ocular Surface Disease

• Dry eye (keratoconjunctivitis sicca): Most frequent cause of conjunctival inflammation; requires treatment of underlying tear film dysfunction 1
• Blepharitis: Another common cause of secondary conjunctival inflammation; treatment must address eyelid margin disease 1
• These conditions often coexist with and exacerbate symptoms of true conjunctivitis 1

Diagnostic Algorithm

Pattern Recognition

• Discharge type: Watery suggests viral or allergic; purulent/mucopurulent suggests bacterial; copious purulent with rapid onset suggests gonococcal 1, 3, 2
• Laterality: Viral often begins unilateral then becomes sequentially bilateral; bacterial may remain unilateral; allergic is typically bilateral from onset 1, 6
• Follicles vs papillae: Follicles (inferior tarsal conjunctiva) suggest viral or chlamydial; papillae suggest allergic or bacterial 1, 6
• Preauricular lymphadenopathy: Present in viral (especially adenoviral) and gonococcal, absent in allergic 1, 3

Critical Red Flags Requiring Immediate Action

• Copious purulent discharge with marked eyelid edema = hyperacute bacterial conjunctivitis requiring immediate systemic ceftriaxone 1g IM/IV without waiting for cultures 3
• Corneal involvement (infiltrates, ulcers) = requires urgent ophthalmology referral and systemic antibiotics 3
• Vesicular rash on eyelids or nose = HSV/VZV requiring antiviral therapy and ophthalmology evaluation 1, 2
• Neonatal conjunctivitis = emergency until gonococcal and chlamydial causes excluded 5

Exposure History

• Recent contact with infected individual, especially in school setting = viral 1
• Recent ocular testing = viral (nosocomial transmission) 1, 5
• Concurrent upper respiratory infection = viral 1
• Sexual activity with genitourinary symptoms = gonococcal or chlamydial 1, 3

Common Pitfalls to Avoid

• Delaying systemic antibiotics in suspected gonococcal conjunctivitis while waiting for culture results can lead to corneal perforation and permanent vision loss 3
• Overlooking serious conditions such as uveitis, acute angle-closure glaucoma, or scleritis that may present with conjunctival hyperemia 6
• Missing corneal involvement on initial examination—always perform careful slit-lamp examination in suspected bacterial cases 3
• Overuse of antibiotics due to clinical ambiguity between viral and bacterial conjunctivitis; consider delayed prescribing for non-severe cases 2, 4
• Failing to identify underlying ocular surface disease (dry eye, blepharitis) that may be the primary problem rather than true infectious conjunctivitis 1