Bacterial Conjunctivitis

Overview & Clinical Features

Bacterial conjunctivitis produces a neutrophilic exudate, and that exudate is what separates it clinically from viral and allergic disease before any culture is sent. The discharge is thick and purulent or mucopurulent rather than watery or stringy, and it dries overnight into crusting that glues the eyelashes and lid margins shut. Patients describe waking with their eyelids stuck together. The conjunctiva itself reacts with a papillary pattern: flat-topped, polygonal elevations with a central vascular tuft, arranged in a mosaic. This is distinct from the lymphoid follicles seen in viral and chlamydial conjunctivitis, and it overlaps with allergic conjunctivitis, so papillae alone don't clinch the diagnosis. Discharge character and the presence or absence of itch do most of that work.

Injection in conjunctivitis of any cause is typically diffuse and most prominent peripherally and in the fornices. Anterior uveitis and keratitis instead produce a circumlimbal flush, a useful distinction when a red eye's underlying cause isn't otherwise obvious. Most uncomplicated bacterial conjunctivitis is a self-limited surface infection with no threat to vision. The exceptions below are exactly the cases where that assumption stops being safe.

Pathogens by Age Group

The dominant organisms differ enough between children and adults that age alone is a useful first clue to likely etiology.

Pediatric

In young children, the trio of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis predominates, often alongside concurrent otitis media. The same organisms that cause middle-ear infection can seed the conjunctiva, so a child with both findings shouldn't prompt additional diagnostic concern.

Adult

In adults, Staphylococcus aureus is the leading bacterial isolate, typically originating from the patient's own eyelid or skin flora rather than an outside source. Lid hygiene is therefore a meaningful part of both treatment and prevention in this group.

Empiric Treatment

Mild-to-moderate, uncomplicated bacterial conjunctivitis is generally treated empirically with a broad-spectrum topical antibiotic, even though many cases resolve without treatment at all. The practical goal is shortening the disease course and cutting transmission, not preventing a vision-threatening outcome, since uncomplicated disease was never going to cause one.

Special Cases

Contact-Lens-Associated (Pseudomonas)

A contact lens wearer with acute bacterial conjunctivitis is treated differently from the start. Pseudomonas aeruginosa is classically associated with contact lens wear, especially extended wear, and is notorious for secreting proteolytic enzymes that can drive rapid, destructive corneal ulceration and perforation if it reaches the cornea. Empiric therapy in this population should therefore reliably cover gram-negative organisms including Pseudomonas. A topical fluoroquinolone is the standard choice, not an agent chosen for typical gram-positive skin-flora coverage alone.

MRSA

Severe or recurrent bacterial conjunctivitis with cultures confirming methicillin-resistant Staphylococcus aureus needs a different agent again. Standard empiric choices like erythromycin are frequently ineffective against resistant strains. Compounded topical vancomycin, or an antibiotic chosen against culture sensitivities, is the appropriate approach once MRSA is confirmed or strongly suspected.

Gonococcal

Neisseria gonorrhoeae causes a hyperacute, rapidly progressive conjunctivitis with copious purulent discharge, seen classically in neonates and in sexually active adults. It is a true ophthalmologic emergency. Unlike most bacteria, gonococcus can invade an intact corneal epithelium, and untreated infection can progress to corneal ulceration and perforation within 24–48 hours. Treatment reflects that urgency: systemic therapy (intramuscular ceftriaxone) is required to eradicate the infection, alongside topical antibiotics and frequent saline irrigation to clear the heavy purulent discharge. Topical therapy alone, without systemic coverage, is not adequate.

Ophthalmia Neonatorum

Conjunctivitis occurring within the first four weeks of life is termed ophthalmia neonatorum, a broad umbrella that includes chemical, gonococcal, chlamydial, and herpetic causes rather than a diagnosis in itself. Standard prophylaxis given to all newborns shortly after delivery is topical erythromycin 0.5% ophthalmic ointment, which has replaced silver nitrate in most regions specifically to prevent gonococcal ophthalmia neonatorum.

Timing is the key clinical clue when prophylaxis fails or wasn't given. Gonococcal ophthalmia neonatorum presents hyperacutely, typically 2–5 days after birth, with severe purulent discharge and eyelid swelling. A neonate this early and this sick should be presumed gonococcal until proven otherwise, and managed with the same systemic-plus-topical urgency described above. Chlamydial conjunctivitis, by contrast, presents later; see the viral & chlamydial conjunctivitis page for that timeline and its distinct systemic treatment requirement.

Two other causes round out the timing picture. Chemical conjunctivitis is the earliest to appear, developing within the first 24 hours as a direct reaction to the prophylactic ointment itself; it is culture-negative and clears on its own within a day or two, so it needs no treatment beyond reassurance. Herpes simplex virus sits at the other end, presenting around days 5–14 with serosanguineous rather than purulent discharge, often alongside vesicular skin lesions near the lids. Most affected infants are born to mothers with no known history of genital herpes, so the diagnosis has to be made on this clinical pattern rather than maternal history. Because it can precede fatal disseminated disease, this presentation warrants urgent intravenous acyclovir rather than watchful waiting.

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