How can bacterial conjunctivitis be distinguished from viral conjunctivitis and what are the first‑line treatments for each?

Distinguishing Bacterial from Viral Conjunctivitis

Bacterial conjunctivitis is characterized by mucopurulent discharge with matted eyelids and a papillary reaction, while viral conjunctivitis presents with watery discharge, follicular reaction on the inferior tarsal conjunctiva, and preauricular lymphadenopathy. 1

Key Clinical Differentiators

Bacterial Conjunctivitis Features

• Mucopurulent or purulent discharge that causes the eyelids to be matted shut, particularly upon waking 1, 2
• Papillary reaction rather than follicular pattern on conjunctival examination 1
• Can be unilateral or bilateral at presentation 1
• Preauricular lymphadenopathy is less common unless caused by hypervirulent organisms like gonococcus 1
• More common in children and may be associated with concurrent bacterial otitis media, sinusitis, or pharyngitis 1
• Mattering and adherence of eyelids on waking, lack of itching, and absence of prior conjunctivitis history are the strongest predictive factors 3

Viral Conjunctivitis Features

• Watery discharge without purulent material 1, 2
• Follicular reaction on the inferior tarsal conjunctiva (not papillary) 1
• Preauricular lymphadenopathy is commonly present, especially with adenoviral infections 1
• Often starts unilateral but becomes sequentially bilateral 1
• Frequently accompanied by concurrent upper respiratory infection 1
• May present with subconjunctival hemorrhages, chemosis, eyelid swelling, and erythema 1
• Self-limited course, typically resolving within 5-14 days 1

Critical Pitfall to Avoid

No single sign or symptom accurately differentiates viral from bacterial conjunctivitis with certainty 2, so clinical judgment must integrate multiple features rather than relying on one finding.

---

First-Line Treatment Approaches

Bacterial Conjunctivitis Treatment

For moderate to severe bacterial conjunctivitis, prescribe a 5-7 day course of broad-spectrum topical antibiotic 1, 4

Antibiotic Selection

• No specific antibiotic is superior for uncomplicated cases—choose the most convenient or least expensive option 1, 4
• Acceptable first-line options include:
  • Erythromycin ointment 1
  • Polymyxin B/trimethoprim drops 1
  • Fluoroquinolones (moxifloxacin, gatifloxacin, ofloxacin) 1, 4
• Reserve fluoroquinolones for moderate to severe cases with copious purulent discharge, marked inflammation, or contact lens wearers at risk for Pseudomonas infection 4
• Fourth-generation fluoroquinolones (moxifloxacin, gatifloxacin) have superior gram-positive coverage including some MRSA strains 4

Mild Bacterial Conjunctivitis

• Mild cases are usually self-limited and may resolve without treatment 1
• However, topical antibiotics shorten disease duration, reduce transmissibility, and allow earlier return to school/work 4, 3

Special Circumstances Requiring Systemic Therapy

• Gonococcal conjunctivitis: Requires systemic antibiotics (ceftriaxone 1g IM plus azithromycin 1g orally) in addition to topical therapy—this is sight-threatening and can cause corneal perforation 1, 4
• Chlamydial conjunctivitis: Requires systemic antibiotics (oral erythromycin or azithromycin) as topical therapy alone is inadequate; evaluate sexual partners 1, 4
• Sexually active patients with bacterial conjunctivitis should have aggressive diagnostic work-up with Gram stain and cultures due to risk of N. gonorrhoeae 5

When to Obtain Cultures

• Obtain conjunctival cultures and Gram staining before initiating treatment if gonococcal infection is suspected 4
• Cultures are generally not needed for uncomplicated cases in immunocompetent patients 4

---

Viral Conjunctivitis Treatment

Avoid antibiotics entirely for viral conjunctivitis—they provide no benefit and may cause unnecessary toxicity 1

Supportive Care Measures

• Artificial tears for symptomatic relief 1, 2
• Cold compresses to reduce discomfort 1
• Topical antihistamines may provide symptomatic relief 1, 2
• Strict hand hygiene and avoidance of contact with others for 10-14 days from symptom onset to prevent transmission 1, 2

When to Consider Corticosteroids

• For severe cases with marked chemosis, lid swelling, pseudomembranes, or subepithelial corneal infiltrates, a short course of topical corticosteroids may be considered 1
• Critical caveat: Corticosteroids require close ophthalmology follow-up with regular monitoring of intraocular pressure and periodic pupillary dilation 1
• Corticosteroids can prolong viral shedding and worsen HSV infections 1

---

Red Flags Requiring Immediate Ophthalmology Referral

Refer urgently if any of the following are present 1, 4:

• Visual loss or decreased vision
• Moderate or severe pain
• Severe purulent discharge
• Corneal involvement
• Conjunctival scarring
• Lack of response to therapy after 3-4 days
• History of herpes simplex virus eye disease
• Immunocompromised state
• Recent ocular surgery 2
• Vesicular rash on eyelids or nose 2

---

Follow-Up Recommendations

• Advise patients to return if no improvement after 3-4 days of appropriate antibiotic therapy for bacterial conjunctivitis 1, 4
• For viral conjunctivitis not on corticosteroids, return if symptoms persist beyond 2-3 weeks 1
• Patients on topical corticosteroids require regular monitoring of intraocular pressure and periodic pupillary dilation 1

---

Common Pitfalls to Avoid

• Do not prescribe antibiotics indiscriminately for viral conjunctivitis—this contributes to antibiotic resistance and causes unnecessary side effects 1, 3
• Do not use topical corticosteroids without close ophthalmology follow-up due to risks of elevated intraocular pressure, cataract formation, and worsening HSV infections 1
• Do not miss gonococcal conjunctivitis—it requires immediate systemic treatment to prevent corneal perforation 1
• Diagnosis of bacterial conjunctivitis is often compromised by prior use of empiric antibacterial therapy before cultures are obtained 5