How do you differentiate between viral and bacterial conjunctivitis?

Differentiating Viral from Bacterial Conjunctivitis

The most reliable way to differentiate viral from bacterial conjunctivitis is through assessment of discharge type, presentation pattern, and associated clinical features, as no single sign or symptom is definitively diagnostic. 1

Key Distinguishing Features

Viral Conjunctivitis

• Discharge characteristics:
  • Watery discharge 2
  • Minimal mucous discharge 2
• Presentation pattern:
  • Often begins unilaterally then becomes sequentially bilateral 2
  • Abrupt onset 2
• Distinctive clinical signs:
  • Preauricular lymphadenopathy (highly suggestive) 2
  • Follicular reaction of inferior tarsal conjunctiva 2
  • Petechial and subconjunctival hemorrhages 2
  • Possible membrane/pseudomembrane formation 2
• Associated findings:
  • Often concurrent upper respiratory infection 2
  • Recent exposure to infected individuals (especially in school settings) 2
  • Self-limited course with improvement within 5-14 days 2

Bacterial Conjunctivitis

• Discharge characteristics:
  • Purulent or mucopurulent discharge 2
  • Eyelids often matted shut, especially upon waking 3
• Presentation pattern:
  • Can be unilateral or bilateral 2
  • Absence of itching 3
• Clinical course:
  • Self-limited in adults, typically resolving in 1-2 weeks without treatment 3
  • More common in children than adults 1
• Absence of preauricular lymphadenopathy (helps distinguish from viral)

Special Considerations

Hyperacute Bacterial Conjunctivitis (Gonococcal)

• Marked eyelid edema
• Marked bulbar conjunctival injection
• Marked purulent discharge
• Preauricular lymphadenopathy
• May have corneal infiltrate or ulcer (often begins superiorly)
• Requires immediate treatment to prevent corneal perforation 2

Herpes Simplex Virus Conjunctivitis

• Usually unilateral
• Watery discharge
• Mild follicular reaction
• May have palpable preauricular node
• Look for vesicular lesions or dendrites (pathognomonic) 2, 4
• Can be bilateral in atopic or immunocompromised patients 2

Diagnostic Algorithm

1. Assess discharge type:

   • Watery → suggests viral
   • Purulent/mucopurulent → suggests bacterial

2. Check for preauricular lymphadenopathy:

   • Present → strongly suggests viral (especially adenoviral)
   • Absent → more consistent with bacterial

3. Evaluate presentation pattern:

   • Sequential bilateral involvement → typical of viral
   • Mattering and adherence of eyelids on waking → strong indicator of bacterial 3

4. Look for associated symptoms:

   • Concurrent upper respiratory symptoms → suggests viral
   • Lack of itching → more consistent with bacterial 3

Clinical Pitfalls to Avoid

1. Overdiagnosis of bacterial conjunctivitis leading to unnecessary antibiotic use. Most cases of conjunctivitis are viral and self-limiting 3.

2. Missing sight-threatening conditions that can mimic conjunctivitis. Refer to ophthalmology if:

   • Severe pain
   • Decreased vision
   • Painful pupillary reaction
   • Recent ocular surgery
   • Vesicular rash on eyelids or nose
   • Immunocompromised state 1, 5

3. Inappropriate corticosteroid use without ruling out herpetic infection, which can worsen the condition 4.

4. Failure to recognize gonococcal conjunctivitis, which requires immediate systemic therapy to prevent corneal perforation 2.

Remember that clinical differentiation is not always definitive, and laboratory testing may be necessary in persistent or severe cases. When in doubt, especially with concerning features or in high-risk patients, ophthalmology referral is warranted.