Bacterial conjunctivitis: diagnosis
Jules L Baum, MD
Boston Eye Associates, Chestnut Hill, Massachusetts, USA
Infections of the conjunctiva, with few exceptions, constitute
a benign, self-limited group of diseases caused by a variety of infectious agents(1). This article, addressed to
the general practitioner, limits itself to a presentation of bacterial conjunctivitis. Except for infections due
and, rarely, a few gram-negative species (e.g., Proteus and Moraxella/Branhamella), bacterial conjunctivitis characteristically resolves in 10-14 days with
antibiotic treatment. Since, with the noted exceptions, it is unusual for a case of acute bacterial conjunctivitis
not to respond rapidly to topical therapy, the choice of drug should be determined in large part by cost and the
potential for an adverse reaction. This characteristic rapid response to treatment is probably due to our ability
to deliver a concentration of drug to the ocular surface much greater than that used in the disk-diffusion assay.
In general, bactericidal rather than bacteriostatic agents are preferable, especially when the patient is immunosuppressed.
Drug delivery by eyedrop is appropriate for daytime use by adults since ointments tend to blur vision. The use
of an ointment, which increases drug contact time, is preferable prior to sleep and in infants and young children
who often cry and squeeze their eyelids thus diluting the drug and reducing drug volume, respectively.
Host Defenses and Risk Factors for Corneal Infection
The conjunctiva, a mucous membrane exposed to the external world, is remarkably resistant to infection. Tears,
in combination with eyelid action, mechanically flush the ocular surface to reduce an ever-present bacterial load.
Further, the tears contain immunoglobulins and components of the complement pathways, lactoferrin, lysozyme and
ß-lysin that help kill microorganisms and decrease their adherence to the ocular surface. Trauma or disease
trigger polymorphonuclear and macrophage release from the conjunctival vessels into the tears. These cellular elements,
combined with the relatively low temperature of the ocular surface and the trapping effect of bacteria by mucus,
serve to limit acute infection. The conjunctiva also contains abundant lymphoid tissue, another component of its
The eyelid margins, and to a lesser degree the conjunctival surface, are populated with a variety of aerobic and
anaerobic organisms.(2) The normal flora consists mainly of staphylococci (>60%;mostly Staphylococcus
epidermidis), diphtheroids, and Propionobacterium
acnes. Local risk factors for conjunctival infection include
trauma, a foreign body, deranged tissue following disease (e.g., erythema multiforme major, ocular cicatricial
pemphigoid) and an infected lacrimal outflow tract.
Much more serious is the risk of corneal infection following conjunctival infection, which carries the potential
for severe permanent loss of vision. Risk factors for corneal infection include prolonged eyelid closure, the use
of soft contact lenses (especially when worn overnight), dry eyes, and corneal epithelial
disruption following disease or trauma (3). It is especially important to instill an appropriate topical antibiotic
as prophylaxis when the cornea is at risk or if there is a "bleb." A bleb, a surgical portal created
to treat glaucoma, is usually located at the superior limbus and is covered only by conjunctiva. This opening provides
the potential for bacterial endophthalmitis to develop. The cornea is at particular risk with eyelid closure, during
sleep, or with corneal exposure, such as may occur in a comatose patient whose eyes may remain open with reduced
blinking. In both of these situations, an antibiotic ointment should be administered. The cornea is also at risk
after Neisseria gonorrhoeae
conjunctivitis in the newborn, because the organism can invade intact epithelium and because of pressure necrosis
of the epithelium due to extensive purulent exudate under the closed eyelid.
Signs and Symptoms
Viral conjunctivitis, most often of adenoviral origin, is the most common form of infectious conjunctivitis. Recognition
of the clinical signs and symptoms which differentiate between viral, allergic and bacterial disease is helpful
in determining whether antibiotic administration is of value (Table 1). General practitioners, well acquainted
with signs such as conjunctival injection and purulence, may have difficulty differentiating follicles from papillae
without magnification. A loupe or a magnifying glass is often adequate.
Follicles, focal lymphoid tissue associated with viral disease, appear as 1-2 mm translucent elevations most easily
seen on the lower palpebral conjunctiva or in the lower fornix, each displaying fine surface vessels. They may
normally be seen along the superior border of the tarsus (e.g., cartilage plate within the upper lid) and on the
tarsal conjunctiva of children. They are also associated with chlamydial (larger than in viral disease), some toxic,
conjunctivitis. Papillae are seen as a myriad of minute, opaque elevations on the tarsal conjunctiva, each with
a central vascular core. Although non-specific, they are common in bacterial disease.
Bacterial conjunctivitis is commonly divided into subtypes based on the degree of purulence (purulent, mucopurulent)
and duration of infection (hyperacute, acute, chronic). Much less often, membrane formation and the presence of
granuloma are used to subtype disease. Although a hyperacute, purulent infection in the newborn is characteristic
of infection due to N. gonorrhoeae,
clinical signs rarely permit the diagnosis of a specific bacterial species in acute disease.
Since the vast majority of cases of bacterial conjunctivitis are of the relatively benign acute type and respond
rapidly to topical therapy, laboratory diagnosis is rarely indicated, except, when necessary, to differentiate
bacterial from other infectious conjunctivitis. When a diagnosis of hyperacute disease is clinically suspect however,
a Gram stain and culture are mandatory. Gonococci are more readily seen on gram stain following scraping of the
inferior palpebral conjunctiva with a platinum spatula than from a swab of the inferior fornix. Material for culture
may be obtained by a brisk calcium alginate swab of the inferior palpebral conjunctiva or fornix. The swab should
be taken before a topical anesthetic is instilled, as these agents and their preservatives may decrease the recovery
of some bacteria.
Hyperacute conjunctivitis has a more rapid and severe onset than that seen in acute conjunctivitis. The overwhelming
preponderance of cases of hyperacute conjunctivitis is due to N.
gonorrhoeae. Conjunctivitis due to Neisseria
meningitidis is seen more commonly in children than in adults
and is a sentinel for potential or concomitant meningococcemia and meningitis. The eye disease from either bacterium
is characterized by lid edema (at times severe enough to close the eye), marked conjunctival injection, chemosis
(conjunctival edema), and a copious purulent discharge. When verbal, the patient often describes moderately severe
ocular discomfort. The incubation period is typically 1-3 days. Most often, the adult has a concomitant genital
infection whereas newborn disease stems from the mother's birth canal.
As stated above, the neonatal cornea is at risk for infection. Systemic therapy is indicated for the treatment
of N. gonorrhoeae and N. meningitidis conjunctivitis
in all age groups to minimize the risk of systemic and corneal infection. Mothers of neonates and sexual partners
of patients with gonococcal conjunctivitis and contacts of patients with meningicoccal conjunctivitis should also
be evaluated and treated. Treatment for N. gonorrhoeae conjunctivitis in the adult consists of a single dose IM injection of ceftriaxone,
1 g.(4,5) In the neonate, a single dose of 25-50 mg/kg IV or IM and a concurrent one-time saline irrigation of
the eye is suggested.(5) Since there may be a chlamydial co-infection, co-treatment should be considered.
Instillation of 1% silver nitrate eyedrops is the standard method of prophylaxis against N.
gonorrhoeae. Saline irrigation immediately following prophylaxis
is not recommended. Recently, povidone-iodine, administered as a 2.5% eyedrop, was found to be more effective as
a prophylactic agent against Chlamydia trachomatous than either silver nitrate or erythromycin.(6) All three agents were equally
effective against N. gonorrhoeae.
Acute conjunctivitis is rapid in onset with infection soon affecting the contralateral eye. Characteristically,
the discharge is mucopurulent and the bulbar conjunctiva is more inflamed than the palpebral conjunctiva. The latter
exhibits a velvety papillary reaction. Symptoms generally subside in 10-14 days, sometimes without specific therapy.
When due to Staphylococcus
the disease may become chronic. Staphylococcus has an affinity to populate the eyelid margin and induce a chronic blepharitis.
Most cases of bacterial conjunctivitis are caused by gram-positive cocci, (2,7) but with residual defects of the
conjunctiva from prior abnormalities, the incidence of gram negative infection increases. Table 2 lists the organisms
In children, Hemophilus influenzae,
and S. aureus
are common pathogens. S. aureus
is the most frequent cause of bacterial conjunctivitis worldwide. S.
pneumoniae infection is self-limited, may occur in epidemics,
is more frequent in temperate climates and winter months and is associated with subconjunctival hemorrhages. Streptococcus pyogenes
infection is associated with pseudomembrane formation, usually on the bulbar conjunctiva. Conjunctivitis due to
biogroup aegyptius, (previously classified as Hemophilus
aegyptius, the Koch-Weeks bacillus), is often epidemic but
may be endemic in warmer climates. It too is associated with subconjunctival hemorrhages. Moraxella/Branhamella, formally seen in urban derelict and alcoholic populations in the United
States, is now rarely encountered. Pseudomonas aeruginosa is an uncommon cause of conjunctivitis except in neonates, who are infrequently
at risk for bacteremia following this infection.(8) When the corneal surface is traumatized concurrent with P. aeruginosa conjunctivitis
in any age group, or when soft contact lenses are worn, the risk of keratitis dramatically increases, with its
potential for corneal scarring and perforation.
Treatment of acute conjunctivitis consists of the administration of a topical antibiotic(s). Table 3 lists the
more common drugs commercially available in the United States. Eyedrops are usually instilled 1-4 hours initially
and ointments 4 times daily. Treatment may be tapered towards the end of the usual 10-14 day course of the infection.
The aminoglycosides, mainstays of treatment for years (except for streptococcal infection), have given way to the
use of the fluoroquinolones. However, bacterial resistance to fluoroquinolones appears to be on the increase (9)
and their use should be restricted, with few exceptions, to tissue-destroying ocular infections. Polymixin B- trimethoprim
eyedrops and bacitracin-polymixin B ointment are effective broad-spectrum drug combinations. Systemic antibiotics
are rarely used for uncomplicated acute conjunctivitis. Exceptions include their use in the treatment of H. influenzae conjunctivitis
in infants and children and the Brazilian clone of H. influenzae, biogroup aegyptius, which is associated with severe systemic consequences.(10)
is, by far, the most common organism associated with chronic bacterial conjunctivitis.(11) S.
epidermidis, part of the normal ocular surface flora, is
a less frequent pathogen. Chronic staphylococcal conjunctivitis, often protracted and associated with chronic staphylococcal
blepharitis, usually responds slowly to topical antibiotic therapy. Bacitracin ointment, after a short initial
period of more frequent application, may have to be applied before sleep for several months to effect a cure. Vancomycin
1% eyedrops, compounded from the parenteral product, may be required following identification of methicillin-resistant
Gram negative infection (see Table 1), associated with disease or treatment that compromises the conjunctiva, may,
at times, be difficult to eradicate even after signs of inflammation have abated. Moraxella/Branhamella is encountered much less frequently than in the past (see above). Chronic
unilateral conjunctivitis may stem from a silent infection of a portion of the lacrimal outflow tract (e.g., canaliculitis,
The widespread use of antibiotics for the treatment of infections of the eye raises concern about the potential
development of bacterial resistance to these drugs. Available data are limited, but nonetheless concerning, with
identification of increasing levels of fluoroquinolone-resistant corneal isolates (7,13,14) as fluoroquinolone
ophthalmic solutions replace aminoglycoside
preparations for treatment of conjunctivitis. Clearly, more research is needed to better assess the scope of this
problem. Mechanisms need to be developed to improve surveillance and to try to reduce the development of resistance
through efficient and judicious antibiotic use.
In summary, bacterial conjunctivitis, ubiquitous and generally easily managed by the general practitioner may on
occasion present special peculiarities and diagnostic or therapeutic difficulties. At times, referral to an ophthalmologist
may be required.
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