Bacterial vs Viral vs Chlamydial vs Allergic Conjunctivitis: Key Clinical Differences
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Overview
Conjunctivitis is inflammation of the conjunctiva and is commonly classified into bacterial, viral, chlamydial, and allergic types. Differentiation is primarily based on discharge, itching, conjunctival reaction (papillae vs follicles), associated systemic symptoms, and response to treatment.
High-Yield Comparison Table
| Feature | Bacterial | Viral | Chlamydial | Allergic |
| Conjunctival reaction | Papillae (inflammatory response) | Follicles (classically viral) | Follicles (chronic/severe cases) | Papillae (“cobblestone” in chronic cases) |
| Itching | Uncommon | Mild | Not prominent | Hallmark symptom (often severe) |
| Tearing | Mild | Watery | Mild–moderate | Increased |
| Discharge | Purulent (yellow/green) | Watery → slightly mucoid | Mucopurulent | Watery or stringy mucus |
| Associated symptoms | Occasionally mild fever or sore throat | Preauricular lymphadenopathy, fever, sore throat | May involve cornea → scarring; systemic symptoms | Sneezing, nasal congestion, allergic rhinitis |
| Laterality | Often unilateral → bilateral | Usually bilateral | Often unilateral, chronic | Usually bilateral |
| Treatment | Topical antibiotics | Supportive ± antivirals (HSV) | Systemic antibiotics | Antihistamine / mast cell stabilizers |
| Precautions | Hand hygiene | Highly contagious | Treat partners | Allergen avoidance |
1. Bacterial Conjunctivitis
Key clues
- Purulent discharge causing eyelids to stick together (especially in the morning)
- Papillae on conjunctiva
- Mild irritation rather than intense itching
Management
- Definitive:
- Erythromycin ophthalmic ointment
- Polymyxin B–trimethoprim drops
- Fluoroquinolones (e.g., ofloxacin, moxifloxacin) for severe cases or contact lens wearers
- Supportive:
- Warm compresses
- Eye hygiene and handwashing
Exam pearl👉 Purulent discharge = think bacterial first
2. Viral Conjunctivitis
Key clues
- Watery discharge
- Follicles on palpebral conjunctiva
- Preauricular lymph node enlargement
- Often follows upper respiratory infection
Management
- Supportive care only (most cases):
- Cool compresses
- Artificial tears
- Antivirals (if HSV suspected):
- Acyclovir or valacyclovir
Precautions
- Highly contagious
- Avoid sharing towels, cosmetics, eye drops
Exam pearl👉 Follicles + preauricular nodes = viral
3. Chlamydial Conjunctivitis
Key clues
- Chronic unilateral conjunctivitis
- Mucopurulent discharge
- Follicular reaction
- Possible corneal involvement → scarring
- Often associated with genital chlamydial infection
Management
- Definitive (systemic therapy required):
- Azithromycin (single oral dose) or
- Doxycycline (7 days)
- Public health:
- Treat sexual partners
- Counsel on STI prevention
Exam pearl👉 Chronic conjunctivitis + mucopurulent discharge = think chlamydia
4. Allergic Conjunctivitis
Key clues
- Severe itching (most important clue)
- Bilateral redness
- Watery or stringy discharge
- Associated allergic rhinitis
Management
- First-line:
- Antihistamine / mast cell stabilizer drops (e.g., olopatadine)
- Adjuncts:
- Cool compresses
- Oral antihistamines (watch for dry eyes)
- Severe cases:
- Short-term topical corticosteroids (ophthalmology supervision only)
Exam pearl👉 If itching dominates → allergic until proven otherwise
Quick Diagnostic Shortcut (Mnemonic)
“PIFA” for Conjunctivitis
- Purulent → Bacterial
- Itching → Allergic
- Follicles + nodes → Viral
- Atypical chronic → Chlamydial
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