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Infectious Disease and Microbiology – Conjunctivitis
Conjunctivitis is an inflammatory reaction of the conjunctiva characterized by hyperemia (red eye) and discharge. It may be acute or chronic and can be infectious or noninfectious. Important infectious forms include trachoma, caused by Chlamydia trachomatis serotypes A–C; inclusion conjunctivitis, caused by sexually transmitted C. trachomatis serotypes D–K; and ophthalmia neonatorum, an acute mucopurulent conjunctivitis occurring within the first month of life.
The incidence of infectious conjunctivitis in primary care settings is significant. In the Netherlands, rates as high as 13.9 cases per 1000 person-years have been reported. In the United States, Chlamydia species are the most common cause of ophthalmia neonatorum (approximately 6.2 per 1000 live births). The incidence of gonococcal ophthalmia neonatorum has decreased dramatically due to prophylaxis at birth. Trachoma remains a major cause of preventable blindness in parts of northern and sub-Saharan Africa, the Middle East, and Asia. Although global prevalence has declined with improved hygiene, millions worldwide remain visually impaired from trachoma.
Risk factors for trachoma include poverty, overcrowding, poor sanitation, and limited access to clean water and healthcare. Transmission occurs via direct contact (hands, towels) and flies. Viral conjunctivitis is often associated with upper respiratory infections or contact with infected individuals. Adult inclusion conjunctivitis may be associated with a history of urethritis, vaginitis, or cervicitis.
Bacterial conjunctivitis develops when normal ocular defense mechanisms are disrupted, such as in tear film abnormalities, ocular surface damage, or systemic immunosuppression. Infectious causes include bacteria (Staphylococcus, Streptococcus, Haemophilus, Neisseria gonorrhoeae, Chlamydia trachomatis, Treponema pallidum, Bartonella henselae), viruses (adenovirus, enterovirus, HSV, VZV), fungi, and parasites. Viral conjunctivitis may present as epidemic keratoconjunctivitis (EKC), pharyngoconjunctival fever, acute hemorrhagic conjunctivitis, or in association with systemic viral illnesses.
Patients typically report tearing, mucous or mucopurulent discharge, eyelid swelling, redness, and foreign-body sensation. Pain is usually minimal and visual acuity only slightly reduced. Gonococcal conjunctivitis presents rapidly with profuse purulent discharge in sexually active adults or neonates. Viral EKC often begins in one eye and spreads to the other, with watery discharge and photophobia.
On examination, conjunctivitis presents with hyperemia, eyelid edema, and discharge. Viral and chlamydial conjunctivitis commonly show a follicular reaction, whereas bacterial and allergic conjunctivitis typically show a papillary reaction. Bacterial infections produce mucopurulent discharge; gonococcal infection produces thick yellow-green exudate. Preauricular lymphadenopathy is common in viral, HSV, gonococcal, and inclusion conjunctivitis. Trachoma leads to chronic follicular inflammation followed by scarring, entropion, trichiasis, and corneal damage. Parinaud oculoglandular syndrome, associated with Bartonella henselae, presents with granulomatous conjunctivitis and regional lymphadenopathy.
Diagnosis is usually clinical. Microbiologic testing is reserved for hyperacute, severe, chronic, or atypical cases. Gram stain may reveal gram-negative intracellular diplococci in gonococcal infection. Chlamydial infection may be diagnosed by Giemsa staining, culture, ELISA, immunofluorescence, or PCR. Viral pathogens can be identified by PCR. Imaging has no role in routine evaluation.
The differential diagnosis includes dry eye disease, allergic conjunctivitis, Stevens–Johnson syndrome, ocular cicatricial pemphigoid, drug-induced conjunctivitis, tumors, and graft-versus-host disease. In neonates, incubation time helps differentiate gonococcal (1–3 days) from chlamydial (5–14 days) conjunctivitis.
Treatment depends on etiology. Viral conjunctivitis generally requires supportive care with artificial tears and cold compresses. Topical steroids may be used cautiously for membranes or pseudomembranes, but are contraindicated in HSV infection, which requires topical antivirals such as trifluridine. Mild bacterial conjunctivitis is treated empirically with topical broad-spectrum antibiotics such as trimethoprim–polymyxin B or fluoroquinolones for 5–7 days. Haemophilus influenzae infections may require oral amoxicillin–clavulanate if systemic involvement is suspected.
Gonococcal conjunctivitis requires systemic ceftriaxone, with additional topical therapy and coverage for possible chlamydial coinfection using oral azithromycin. Adult inclusion conjunctivitis is treated with oral azithromycin and topical erythromycin or tetracycline ointment. Trachoma is treated with single-dose oral azithromycin and prolonged topical antibiotic therapy. Ophthalmia neonatorum requires systemic treatment based on the organism: ceftriaxone for gonococcal infection, oral erythromycin for chlamydial infection, and intravenous acyclovir for HSV infection.
Most cases of infectious conjunctivitis resolve within three weeks. Exceptions include untreated chlamydial infection, which may become chronic. Trachoma can lead to scarring, entropion, trichiasis, and corneal opacity, resulting in blindness. Viral EKC may cause subepithelial corneal infiltrates requiring prolonged steroid therapy. Neonates are at risk for systemic complications such as sepsis, meningitis, or pneumonia depending on the causative organism.
Preventive measures include hand hygiene, avoidance of sharing personal items, neonatal prophylactic ointment after birth, and treatment of sexual partners in chlamydial conjunctivitis. Public health interventions have significantly reduced the global burden of trachoma, though it remains an important cause of preventable blindness in endemic regions.
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