Konjungtivitis Bakteri

01Pathophysiology

Bacterial conjunctivitis develops when pathogenic bacteria breach the normal ocular surface defenses, which include the tear film (containing lysozyme, lactoferrin, and immunoglobulin A), constant mechanical clearance by blinking, and the intact conjunctival epithelium. Once organisms adhere to and colonize the conjunctiva, they trigger an acute neutrophil-predominant inflammatory response, which explains the characteristic purulent (pus-filled) discharge. The accumulation of neutrophils, fibrin, and cellular debris overnight is what causes the eyelids to be matted shut on awakening, a classic vignette clue.

The conjunctival vasodilation produces the diffuse bulbar and palpebral injection, distinguishing it from the perilimbal "ciliary flush" of keratitis or iritis. Because the inflammation remains superficial and does not involve the cornea, iris, or deeper structures, visual acuity is preserved and photophobia is absent. This is a high-yield discriminator: any red eye with vision loss, severe pain, or photophobia is not simple conjunctivitis and warrants urgent evaluation for sight-threatening pathology.

Different organisms produce distinct clinical patterns. Neisseria gonorrhoeae is unique because it can penetrate intact corneal epithelium, making it a true ophthalmologic emergency that can cause corneal perforation within 24 to 48 hours. Chlamydia trachomatis is an obligate intracellular pathogen that produces a more indolent, chronic follicular reaction. In contact lens wearers, Pseudomonas aeruginosa secretes proteolytic exotoxins that can rapidly progress to bacterial keratitis with corneal ulceration, which is why these patients always require antipseudomonal coverage.

02Classification and Clinical Manifestation

03Diagnostic Workup

For the routine, otherwise healthy patient with a typical mucopurulent red eye, bacterial conjunctivitis is a clinical diagnosis and no laboratory testing is required. Empiric topical antibiotic therapy is appropriate.

The best initial test when laboratory workup is indicated is Gram stain of conjunctival scrapings, which provides rapid information about the likely organism and allows targeted therapy. The most accurate/confirmatory test is bacterial culture on blood and chocolate agar, which identifies the organism definitively and provides antimicrobial sensitivities. Laboratory workup is indicated in any of the following: hyperacute presentation (rule out gonococcal disease), neonatal conjunctivitis, contact lens wearers (rule out Pseudomonas), immunocompromised patients, severe or refractory disease, and any patient with vision changes or suspected keratitis.

For suspected chlamydial conjunctivitis, the test of choice is nucleic acid amplification testing of conjunctival swabs, which is more sensitive than Giemsa stain. Coexisting genital infection should be evaluated. Fluorescein staining should always be performed if there is any concern for corneal involvement; a positive uptake pattern (especially dendritic or ulcerative) changes the diagnosis to keratitis and changes management entirely.

04Management and Treatment

For the otherwise healthy patient with routine acute bacterial conjunctivitis, topical antibiotic therapy shortens the duration of symptoms and reduces transmission, although most cases would resolve spontaneously within 1 to 2 weeks. Trimethoprim-polymyxin B drops and erythromycin ointment are the typical first-line agents because of cost, efficacy, and minimal resistance concerns. Adjunctive measures include warm compresses to loosen crusting, frequent handwashing, avoiding eye rubbing, and discarding contaminated cosmetics.

Contact lens wearers require a fluoroquinolone such as moxifloxacin or ciprofloxacin because of the risk of Pseudomonas aeruginosa, which can rapidly cause bacterial keratitis and corneal melt. Contact lens use must be discontinued until the infection has cleared and the patient is asymptomatic for at least 24 hours after completing antibiotics.

Hyperacute gonococcal conjunctivitis is an ophthalmologic emergency. The next best step is intramuscular ceftriaxone 1 g as a single dose along with copious saline lavage to remove the purulent discharge. Empiric coverage for coexisting chlamydial infection with azithromycin should also be given, and the patient should be evaluated for other sexually transmitted infections. Failure to treat promptly can result in corneal perforation and permanent vision loss.

Chlamydial conjunctivitis in adults is treated with oral azithromycin 1 g single dose or doxycycline 100 mg twice daily for 7 days. Topical therapy alone is inadequate because of the systemic nature of the infection and the presence of concurrent genital tract infection in most patients. Sexual partners require evaluation and treatment.

In neonatal conjunctivitis, the timing of onset narrows the differential. Onset on day 1 suggests chemical conjunctivitis from silver nitrate prophylaxis (now largely replaced). Onset on day 2 to 5 suggests gonococcal disease, treated with parenteral ceftriaxone. Onset on day 5 to 14 suggests chlamydial disease, treated with oral erythromycin because topical therapy does not prevent the associated chlamydial pneumonia. Important contraindication: oral erythromycin in neonates carries a risk of infantile hypertrophic pyloric stenosis, particularly in those under 2 weeks of age, so parents should be counseled to watch for projectile vomiting.

Topical corticosteroids should never be prescribed empirically for a red eye because they can worsen undiagnosed herpetic keratitis and lead to corneal scarring or perforation.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common error on this topic is failing to recognize the red flags that move the diagnosis away from simple conjunctivitis. A patient with a red eye who has vision loss, photophobia, severe pain, or ciliary flush does not have conjunctivitis, and choosing topical antibiotics for such a patient is the wrong answer regardless of how attractive the bacterial features appear. The core competency tested here is the ability to triage the red eye and recognize sight-threatening pathology (keratitis, uveitis, angle-closure glaucoma) hiding behind a vignette that looks superficially like a routine conjunctivitis.

The second classic trap is the contact lens wearer with a red eye. Even if the vignette emphasizes mucopurulent discharge and looks like standard bacterial conjunctivitis, the correct management is a fluoroquinolone with Pseudomonas coverage, not erythromycin or trimethoprim-polymyxin. Missing this leads to bacterial keratitis and corneal perforation. The question stem will often plant subtle clues such as "wears soft contact lenses overnight" or "rinses lenses with tap water."

The third high-yield trap is the hyperacute presentation. A vignette describing onset over hours with profuse, copious purulent discharge in a sexually active adult or in a neonate at day 2 to 5 is gonococcal conjunctivitis, which requires systemic ceftriaxone, not topical drops. The distinction matters because gonococcus can penetrate intact corneal epithelium and cause perforation within 24 to 48 hours.

Fourth, the discharge type is the highest-yield differentiating feature between the three common conjunctivitides: purulent and matted equals bacterial, watery with preauricular node equals viral, and itchy with stringy mucus equals allergic. If the vignette says "itchy," the answer is allergic, even if some bacterial features are mentioned as distractors.

Finally, in neonatal conjunctivitis, the timing of onset is the discriminator, and the chlamydial neonate requires oral erythromycin (not topical) because of concurrent pneumonia risk, while remembering the association with infantile hypertrophic pyloric stenosis is a frequent secondary testing point.