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Infectious Conjunctivitis (Pink Eye)

What is Infectious Conjunctivitis?

Infectious conjunctivitis, commonly known as “pink eye,” is an inflammation of the conjunctiva—the thin, transparent membrane that covers the white part of the eye (the sclera) and lines the inside of the eyelids. When this tissue becomes infected, it turns red, swells, and produces a discharge that may be watery, mucoid, or purulent. The condition is highly contagious, especially in crowded settings such as schools, daycare centers, and workplaces.

While the term “conjunctivitis” simply describes inflammation of the conjunctiva, adding “infectious” tells us that a virus, bacteria, or, less commonly, a parasite is the underlying cause. Non‑infectious forms (e.g., allergic or irritant conjunctivitis) look similar but do not spread from person to person.

Common Causes

Most cases of infectious conjunctivitis are caused by one of the following agents. Some are viral, others bacterial, and a few are less common but important to recognize.

• adenovirus – the most frequent viral cause; often linked to colds, sore throat, or “upper‑respiratory‑tract infection” outbreaks.
• enterovirus (e.g., Coxsackievirus) – can cause a more severe, watery discharge and may be associated with hand‑foot‑mouth disease.
• herpes simplex virus (HSV) – produces a painful, ulcerative form; more common in adults with prior HSV infections.
• varicella‑zoster virus (VZV) – can cause “herpes zoster ophthalmicus” when the virus reactivates in the trigeminal nerve.
• bacterial pathogens – most commonly Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. In newborns, Neisseria gonorrhoeae or Chlamydia trachomatis are critical considerations.
• chlamydial infection (C. trachomatis) – often presents in infants as “inclusion conjunctivitis” and in adults as chronic, mucopurulent discharge.
• mycoplasma pneumoniae – an atypical bacterial cause that may accompany respiratory symptoms.
• parasites – rare; Acanthamoeba can cause a severe keratitis that mimics conjunctivitis, especially in contact‑lens users.
• co‑infection with respiratory viruses – influenza, respiratory syncytial virus (RSV), or COVID‑19 can precipitate conjunctival inflammation.
• neonatal transmission – during childbirth from an infected mother (e.g., gonococcal or chlamydial infection).

Associated Symptoms

Infectious conjunctivitis rarely acts alone; other ocular and systemic signs often accompany it.

• Redness that starts at the inner corner of the eye and spreads outward.
• Eye discharge:
  • Watery (viral) – “scratchy” feeling.
  • Thick, yellow‑green (bacterial) – may crust over the lashes, especially after sleep.
• Itching or burning sensation (more common with viral infections).
• Gritty or foreign‑body sensation.
• Swollen eyelids.
• Blurred vision that typically resolves after the discharge is cleared.
• Photophobia (light sensitivity) – usually mild.
• Fever, sore throat, or upper‑respiratory symptoms (more common with viral causes).
• In newborns: excessive tearing, eyelid swelling, and a sticky discharge that may be yellow or green.

When to See a Doctor

Most cases of viral conjunctivitis improve on their own within 1–2 weeks, but certain situations require prompt medical evaluation.

• Symptoms last longer than 7–10 days without improvement.
• Severe pain, intense redness, or swelling that spreads beyond the conjunctiva.
• Vision becomes blurry and does not clear after wiping away discharge.
• Sensitivity to light is marked, or you notice halos around lights.
• Eye discharge is thick, pus‑like, and does not improve with simple hygiene.
• History of recent trauma, eye surgery, or contact‑lens wear (risk of bacterial keratitis).
• Newborns or infants with red eyes—especially if accompanied by fever or lethargy.
• Immunocompromised individuals (e.g., chemotherapy, HIV) develop conjunctivitis.
• Any suspicion of gonococcal or chlamydial infection (high‑risk sexual exposure, newborn with ophthalmic symptoms).

Diagnosis

Diagnosis is primarily clinical, based on history and physical exam, but certain tests help differentiate viral from bacterial or atypical causes.

1. Visual inspection – The clinician looks for characteristic patterns of redness, discharge type, and eyelid swelling.
2. Eye swab for culture – Indicated when bacterial infection is suspected, especially in severe cases, contact‑lens wearers, or when symptoms persist.
3. Gram stain – Provides rapid insight into bacterial morphology (gram‑positive vs. gram‑negative).
4. Polymerase chain reaction (PCR) – Detects viral DNA/RNA (adenovirus, HSV, VZV, SARS‑CoV‑2) and can be useful in outbreak settings.
5. Conjunctival scrapings – Used for atypical organisms like Chlamydia or Mycoplasma.
6. Fluorescein staining – A dye that highlights corneal abrasions or ulcerations that may accompany severe infection.
7. Blood tests – Rarely needed, but a complete blood count (CBC) can support a systemic infection if indicated.

Treatment Options

Treatment depends on the identified or presumed cause.

Viral Conjunctivitis

• Most cases are self‑limited; supportive care is key.
• Cold compresses applied for 5–10 minutes, 3–4 times daily to reduce discomfort.
• Artificial tears (preservative‑free) to alleviate dryness.
• Topical antihistamine or mast‑cell stabilizer drops can help with itching.
• Antiviral therapy (e.g., topical trifluridine or oral acyclovir) is reserved for HSV or VZV infections.
• Strict hand‑washing and avoiding contact lens wear until resolution.

Bacterial Conjunctivitis

• First‑line: Topical antibiotic drops or ointments (e.g., erythromycin ophthalmic ointment, fluoroquinolone drops such as moxifloxacin for more resistant strains).
• Course typically lasts 5‑7 days; improvement should be seen within 24‑48 hours.
• For neonates with suspected gonococcal infection: Immediate intravenous ceftriaxone is required, followed by topical erythromycin.
• For chlamydial conjunctivitis: Oral azithromycin (single 1‑g dose) or a 7‑day course of doxycycline.
• In contact‑lens wearers, discontinue lens use and consider a broader‑spectrum antibiotic plus a thorough lens cleaning protocol.

Adjunctive Home Care (All Forms)

• Wash hands frequently with soap and water for at least 20 seconds.
• Avoid touching or rubbing the eyes.
• Use a clean, warm (not hot) compress to loosen crusted discharge.
• Discard or launder pillowcases, towels, and washcloths daily.
• Do not share eye cosmetics, contact‑lens solutions, or eye drops.
• Replace eye makeup every 3 months; discard any products that may have been contaminated.

Prevention Tips

Because infectious conjunctivitis spreads easily, simple hygiene measures dramatically reduce risk.

• Wash hands often, especially after coughing, sneezing, or using the bathroom.
• Use disposable tissues; discard immediately and wash hands afterward.
• Avoid sharing towels, pillowcases, cosmetics, or eye‑care products.
• If you wear contact lenses, follow the manufacturer’s cleaning schedule and replace lenses as directed.
• Stay home from school, work, or daycare until 24 hours after symptoms improve (especially for bacterial cases with discharge).
• Clean frequently touched surfaces—doorknobs, light switches, shared computers—with EPA‑approved disinfectants.
• For newborns, apply prophylactic erythromycin ointment to the eyes within one hour of birth (standard in many countries).
• Vaccinate against preventable viral illnesses (e.g., measles, influenza) that can have ocular manifestations.

Emergency Warning Signs

Key Takeaways

Infectious conjunctivitis is a common, usually self‑limited eye condition that can be caused by viruses, bacteria, or less often parasites. Prompt recognition, good hygiene, and appropriate treatment—especially for bacterial or atypical forms—help relieve symptoms, curb spread, and prevent complications. Always consult a healthcare professional if symptoms are severe, prolonged, or accompanied by vision changes.

Sources: Mayo Clinic, CDC, National Institutes of Health (NIH), World Health Organization (WHO), Cleveland Clinic, American Academy of Ophthalmology, Ophthalmology journals (e.g., *JAMA Ophthalmology*, *Ophthalmology*).

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