Confusable diagnoses · PANCE / PANRE

Bacterial Conjunctivitis vs Viral Conjunctivitis

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Bacterial Conjunctivitis and Viral Conjunctivitis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Bacterial Conjunctivitis vs Viral Conjunctivitis at a glance

  • Bacterial Conjunctivitis: Acute purulent conjunctival infection — most often self-limited; topical antibiotics shorten course.
  • Viral Conjunctivitis: Highly contagious viral inflammation of conjunctiva — typically adenovirus; supportive care only.

Try two board-style questions on Bacterial Conjunctivitis vs Viral Conjunctivitis

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Question 1EENTMedium
A 9-year-old girl presents with two days of bilateral eye redness and copious yellow-green discharge that mats her eyelashes together each morning. She denies pain, photophobia, or vision changes. On examination, both conjunctivae are diffusely injected with mucopurulent discharge at the lid margins. Visual acuity is 20/20 bilaterally, and the cornea is clear with no fluorescein uptake. She wears no contact lenses. Which of the following is the most appropriate treatment?
  • ATopical acyclovir ointment
  • BTopical ketotifen drops
  • CTopical erythromycin ointment
  • DOral amoxicillin-clavulanate
Reveal answer & full explanation
Correct answer: C — Topical erythromycin ointment
  • ATopical acyclovir ointment
  • BTopical ketotifen drops
  • CTopical erythromycin ointment✓
  • DOral amoxicillin-clavulanate

Why Topical erythromycin ointment is correct

  • This presentation is acute bacterial conjunctivitis: bilateral mucopurulent discharge with matted lashes and no corneal involvement.
  • Most common pathogens in children are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
  • First-line management for uncomplicated, non-contact-lens-wearer bacterial conjunctivitis is a topical antibiotic such as erythromycin ointment or polymyxin-trimethoprim drops, which shortens duration and reduces transmission.
  • Topical erythromycin provides broad gram-positive and limited gram-negative coverage appropriate for this presentation.

Why the others are wrong

  • D) Oral amoxicillin-clavulanate — reserved for suspected H. influenzae conjunctivitis-otitis syndrome or gonococcal/chlamydial disease, not routine cases.
  • A) Topical acyclovir ointment — treats herpes simplex keratitis, which presents with unilateral pain, photophobia, and dendritic corneal staining.
  • B) Topical ketotifen drops — a mast-cell stabilizer/antihistamine used for allergic conjunctivitis, which features itching and watery discharge rather than purulent exudate.

Additional high-yield points

  • Contact lens wearers require pseudomonal coverage (fluoroquinolone) instead.
Question 2EENTEasy
A 26-year-old preschool teacher has 3 days of redness, burning, and watery discharge in the right eye that spread to the left eye yesterday. She had a sore throat and low-grade fever last week, and two children in her classroom have had red eyes. Visual acuity is 20/20 in each eye. Both eyes show diffuse conjunctival injection with scant watery discharge, and the corneas are clear. Which additional physical examination finding is most likely to be present?
  • AClustered vesicles along the upper eyelid margin
  • BStringy mucus strands with conjunctival chemosis
  • CTender preauricular lymphadenopathy on the right
  • DEyelid margin crusting with collarettes at the lashes
Reveal answer & full explanation
Correct answer: C — Tender preauricular lymphadenopathy on the right
  • AClustered vesicles along the upper eyelid margin
  • BStringy mucus strands with conjunctival chemosis
  • CTender preauricular lymphadenopathy on the right✓
  • DEyelid margin crusting with collarettes at the lashes

Why Tender preauricular lymphadenopathy on the right is correct

  • Adenoviral conjunctivitis is the most common infectious conjunctivitis and is suggested here by a recent upper respiratory prodrome, sick contacts in a daycare setting, watery discharge, and sequential involvement of the second eye.
  • The adenovirus drains to the preauricular node, so a palpable tender node just anterior to the tragus on the more affected side is the classic corroborating finding and is uncommon in bacterial or allergic disease.
  • Other supportive findings are follicles on the inferior tarsal conjunctiva and a gritty burning sensation with preserved acuity.
  • Management is supportive with cool compresses and strict hand hygiene, and patients remain contagious for roughly 10 to 14 days while tearing persists; antibiotic drops add nothing.
  • Tender preauricular lymphadenopathy on the right — correct, regional adenopathy tracks with adenoviral infection.

Why the others are wrong

  • Clustered vesicles along the upper eyelid margin — the lid finding of herpes simplex blepharoconjunctivitis, which is usually unilateral and is not the pattern of a red-eye outbreak among classroom contacts after a febrile pharyngitis; bilateral sequential involvement with a URI prodrome and sick contacts points to adenovirus.
  • Stringy mucus strands with conjunctival chemosis — typical of allergic conjunctivitis, which is bilateral from the outset, intensely itchy, and seasonal or exposure related rather than preceded by a febrile URI.
  • Eyelid margin crusting with collarettes at the lashes — blepharitis, a chronic relapsing lid margin disease with scurf and lash debris, not a 3 day contagious red eye.
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Side-by-side comparison

FeatureBacterial ConjunctivitisViral Conjunctivitis
At a glanceAcute purulent conjunctival infection — most often self-limited; topical antibiotics shorten course.Highly contagious viral inflammation of conjunctiva — typically adenovirus; supportive care only.
Classic presentationBilateral mucopurulent discharge with eyelids matted shut on awakening and normal vision in a school-age child.; Eye redness, often beginning unilateral and spreading to fellow eye in 1-2 days; Mucopurulent (yellow/green) discharge throughout the day; Eyelids matted/stuck shut on awakening; Foreign body or 'gritty' sensation; Minimal or…Watery red eye with follicular reaction, ipsilateral preauricular lymphadenopathy, and recent URI in an adult.; Acute red eye, often beginning unilateral and spreading to fellow eye within days; Watery discharge — clear, profuse; Foreign body or gritty sensation, burning; Mild eyelid swelling and crusting (less than bacterial); Recent…
Workup / key labsMost cases: clinical diagnosis; no testing needed; Gram stain and culture if: hyperacute presentation, contact lens wearer, severe disease, neonate, immunocompromised, treatment failure; NAAT for Chlamydia trachomatis and Neisseria gonorrhoeae in adults with suspected STI conjunctivitis or in neonatal conjunctivitisClinical diagnosis usually sufficient; Rapid adenovirus antigen test (e.g., AdenoPlus) available in some settings — useful for outbreak control and to avoid unnecessary antibiotics; Viral culture or PCR rarely needed; consider for atypical, severe, or HSV/VZV suspected cases; NAAT for chlamydia/gonorrhea if STI exposure or chronic…
ImagingSlit-lamp examination if any pain, photophobia, decreased vision, contact lens wear, or treatment failure — exclude keratitis or iritis; Fluorescein staining if corneal involvement suspectedSlit-lamp examination with fluorescein staining if photophobia, decreased vision, contact lens wear, or corneal involvement suspected — looks for dendrites (HSV), subepithelial infiltrates (EKC), or pseudodendrites (VZV)
First-line treatmentMost uncomplicated bacterial conjunctivitis is self-limited; topical antibiotics shorten course and reduce transmission; Topical ocular antibiotic — erythromycin ophthalmic ointment 0.5%, polymyxin B/trimethoprim drops, or moxifloxacin/ofloxacin drops × 5-7 days; Avoid topical aminoglycosides (gentamicin, tobramycin) as first line —…Supportive care — viral conjunctivitis is self-limited (1-3 weeks); Cool compresses to reduce swelling; Artificial tears for lubrication and symptom relief; Strict hygiene: hand washing, no shared towels/pillows/eye drops, no cosmetics, no contact lens wear until resolved; Stay home from school/work until tearing and discharge resolve…

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Full outlines

Bacterial Conjunctivitis Viral Conjunctivitis All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.