How do you differentiate between bacterial and viral conjunctivitis?

Differentiating Bacterial from Viral Conjunctivitis

Bacterial conjunctivitis characteristically presents with mucopurulent discharge and matted eyelids upon waking, while viral conjunctivitis typically shows watery discharge with a follicular reaction on the inferior tarsal conjunctiva and preauricular lymphadenopathy. 1

Key Clinical Distinguishing Features

Discharge Characteristics

• Bacterial: Purulent or mucopurulent discharge with eyelids matted shut, particularly in the morning 1, 2
• Viral: Watery, serous discharge without matting 1, 2

Conjunctival Reaction Pattern

• Bacterial: Papillary reaction on tarsal conjunctiva 1
• Viral: Follicular reaction specifically on the inferior tarsal conjunctiva, which is a hallmark finding 1

Lymph Node Involvement

• Viral: Preauricular lymphadenopathy is common, especially with adenoviral infections 1
• Bacterial: Preauricular lymphadenopathy is less common unless caused by hypervirulent organisms like gonococcus 1

Laterality and Onset

• Viral: Abrupt onset, often starting unilateral but frequently becomes sequentially bilateral within days 1
• Bacterial: Can be unilateral or bilateral at presentation 1

Associated Symptoms

• Viral: Often accompanied by concurrent upper respiratory infection symptoms; may have subconjunctival hemorrhages, chemosis, and marked eyelid swelling 1
• Bacterial: May be associated with concurrent bacterial otitis media, sinusitis, or pharyngitis, particularly in children 1

Important Clinical Caveats

No Single Pathognomonic Sign

While these features are helpful, no single sign or symptom accurately differentiates viral from bacterial conjunctivitis with 100% certainty 2. The strongest predictors for bacterial etiology are matting and adherence of eyelids on waking, lack of itching, and absence of prior conjunctivitis history 3.

Severe Viral Mimics Bacterial

Severe adenoviral conjunctivitis can present with marked eyelid swelling and erythema that may resemble preseptal cellulitis or severe bacterial infection, creating diagnostic confusion 4. In these cases, the presence of follicles and preauricular lymphadenopathy helps identify viral etiology 1.

Age-Related Patterns

• Bacterial conjunctivitis is more common in children 2
• Viral and allergic conjunctivitis are more common in adults 2

Algorithmic Approach to Diagnosis

Step 1: Assess discharge type

• Purulent/mucopurulent with matted lids → likely bacterial 1
• Watery discharge → likely viral or allergic 1

Step 2: Examine tarsal conjunctiva

• Papillary reaction → suggests bacterial 1
• Follicular reaction (inferior tarsal) → suggests viral 1

Step 3: Check for preauricular lymphadenopathy

• Present → strongly suggests viral 1
• Absent → does not rule out either, but less typical for viral 1

Step 4: Assess associated symptoms

• Upper respiratory symptoms → viral 1
• Bacterial otitis/sinusitis → bacterial 1
• Itching predominant → allergic (different entity) 1

Management Implications Based on Differentiation

If Viral

• Avoid antibiotics entirely as they provide no benefit and may cause toxicity 1
• Supportive care with artificial tears, cold compresses, and topical antihistamines for symptom relief 1
• Patient education about high contagiousness for 10-14 days from symptom onset 1
• Self-limited course, typically resolving within 5-14 days 1

If Bacterial

• Mild cases are self-limited and may resolve without treatment 1
• For moderate to severe cases, prescribe a 5-7 day course of broad-spectrum topical antibiotic 1
• No specific antibiotic has proven superiority; choose based on convenience and cost 1

Red Flags Requiring Immediate Ophthalmology Referral

• Visual loss or decreased vision 1
• Moderate or severe pain 1
• Corneal involvement 1
• History of HSV eye disease 1
• Immunocompromised state 1
• Vesicular rash on eyelids (suggests HSV) 1
• Severe purulent discharge with marked lid edema (consider gonococcal) 1