Bacterial conjunctivitis is common in children and adults presenting with a red eye. Although most cases are self-limited, appropriate antimicrobial treatment accelerates resolution and reduces complications. It is critical to differentiate bacterial conjunctivitis from other types of conjunctivitis and more serious vision-threatening conditions so that patients can be appropriately treated and, if necessary, referred to an ophthalmologist.
This paper is an overview of how to diagnose and manage bacterial conjunctivitis for the office-based internist.
CAUSES VARY BY AGE
In neonates, conjunctivitis is predominantly bacterial, and the most common organism is Chlamydia trachomatis. Chlamydial conjuctivitis typically presents with purulent unilateral or bilateral discharge about a week after birth in children born to mothers who have cervical chlamydial infection. Many infants with chlamydial conjunctivitis develop chlamydial pneumonitis: approximately 50% of infants with chlamydial pneumonitis have concurrent conjunctivitis or a recent history of conjunctivitis.1
Neisseria gonorrhoeae is a rare cause of neonatal conjunctivitis. The onset is somewhat earlier than in chlamydial conjunctivitis, ie, in the first week of life, and this organism classically causes severe “hyperacute” conjunctivitis with profuse discharge and may result in corneal involvement and perforation. Routine antibiotic prophylaxis at birth has markedly reduced its incidence and complications.
Other bacteria that can cause neonatal conjunctivitis include Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae.2
In children, bacterial conjunctivitis is most often caused by H influenzae or S pneumoniae, which accounted for 29% and 20% of cases, respectively, in a prospective study in Israel.3 Whether patients had been vaccinated against H influenzae in this study is unclear.
H influenzae conjunctivitis spreads easily in schools and households. It is associated with concurrent upper respiratory tract infections and otitis media (conjunctivitis-otitis syndrome): 45% to 73% of patients with purulent conjunctivitis also have ipsilateral otitis media.4
S pneumoniae, the second most common cause of bacterial conjunctivitis in children, is a common cause in epidemic outbreaks among young adults. Newly described unencapsulated pneumococcal strains caused outbreaks that affected 92 recruits at a military training facility and 100 students at Dartmouth University.5S pneumoniae is also associated with conjunctivitis-otitis syndrome, accounting for approximately 23% of culture-proven cases.4
Moraxella species, S aureus, and coagulase-negative staphylococci are less common causes of bacterial conjunctivitis in children.6–8
In adults, the most common causes of bacterial conjunctivitis are S aureus and H influenzae. Conjunctivitis caused by S aureus is often recurrent and associated with chronic ble-pharoconjunctivitis (inflammation of the eyelid and conjunctiva). The conjunctivae are colonized by S aureus in 3.8% to 6.3% of healthy adults.9–11 In addition, about 20% of people normally harbor S aureus continually in the nasal passages, and another 60% harbor it intermittently; in both cases, the bacteria may be a reservoir for recurrent ocular infection.12
Other organisms that commonly cause conjunctivitis in adults are S pneumoniae, coagulase-negative staphylococci, and Moraxella and Acinetobacter species.13
Little has been published about hospital-acquired conjunctivitis. In a neonatal intensive care unit, the most common organisms isolated in patients with conjunctivitis were coagulase-negative staphylococci, S aureus, and Klebsiella species.14 We found that about 30% of children who developed bacterial conjunctivitis after 2 days of hospitalization at Cleveland Clinic harbored gram-negative organisms. In addition, in patients who were found to have conjunctivitis caused by Staphylococcus species, the rate of methicillin resistance was higher in those hospitalized for more than 2 days than those with Staphylococcus species who were hospitalized for less than 2 days. This suggests that the bacterial pathogens encountered in hospitalized children with conjunctivitis differ from those found in the outpatient setting.15
EYE DISORDERS PREDISPOSE TO INFECTION
The conjunctiva is a transparent membrane that covers the sclera and lines the inside of the eyelid. It is a protective barrier against invading pathogens and lubricates the ocular surface by secreting components of the tear film (although the lacrimal glands contribute more to the tear film).
Several unique anatomic and functional features of the ocular surface help prevent bacterial infection in the healthy eye. The tear film contains secreted immunoglobulins, lysozyme, complement, and multiple antibacterial enzymes, and it is continuously being flushed and renewed, creating a physically and immunologically adverse environment for bacterial growth.
Disorders involving the eyelids or tear film such as chronic dry eye and lagophthalmos (in which the eye cannot close completely) may predispose the eye to frequent infections. Also, an adjacent focus of infection, such as inflammation of the lacrimal gland (dacryocystitis), can cause recurrent or chronic conjunctivitis.16