Conjunctivitis is defined as “inflammation of the conjunctiva,” and its etiology can be grouped into three broad categories: infectious, immunologic, or irritative. This column will not address either of the latter two categories (which include systemic diseases and allergic conjunctivitis), but will cover the more common etiologies, bacterial and viral. The diagnosis and treatment of bacterial and viral conjunctivitis is an area of controversy, and hopefully I can shed some light on a topic that still has no solid evidence-based literature.
Because the diagnosis of conjunctivitis is made clinically, one needs to rule out the other causes of a red eye by both history and physical. In conjunctivitis, the conjunctiva becomes red and inflamed. The patient will complain of a red eye, discharge, mild pain or a foreign-body sensation, or pruritis. Any change in visual acuity should expand the differential to more serious causes of the “red eye.” The exam will reveal infected conjunctivae with some degree of discharge (watery white to thick green-yellow) and occasionally enlarged pre-auricular nodes. If there is any fluorescein uptake, then a corneal abrasion, corneal foreign bodies, corneal ulcers, keratoconjunctivitis or herpetic conjunctivitis become the more likely causes.
Topical anesthetics may lead to corneal scarring, and topical steroids may exacerbate herpetic conjunctivitis
The next step is to try to determine if it is bacterial or viral, which by exam is not reliable. Some exam findings that make viral more likely are a follicular response (white-grey 1 mm elevations on the conjunctiva) or enlarged pre-auricular nodes and thinner discharge. None of these can completely or reliably confirm a viral etiology, however.
Herpes virus deserves special mention. With this virus, conjunctivitis will have fluorescein uptake (a stellate pattern), and if found, should prompt an ophthalmology consult. The most common virus is adenovirus, which has several serotypes, one of which is associated with pharyngitis and another with keratoconjunctivitis (which has corneal involvement). Coxsackie and enterovirus are responsible for a smaller percentage of cases. It can be either unilateral or bilateral, but if bilateral, the patient will often state that the symptoms began in one eye. There is white-yellow discharge and morning crusting. Often there are associated upper respiratory symptoms.
Bacterial vs. Viral
Bacterial conjunctivitis is less common than viral, and although there are several clinical findings that can suggest bacterial over viral, it is difficult to differentiate between the two. Thicker discharge, no enlarged pre-auricular nodes, and a concomitant otitis media in children suggest a bacterial etiology. (Pediatr Ann 1993;22:353.) The organisms most commonly responsible for bacterial conjunctivitis are pneumococcus, H. influenzae and S. aureus. Two bacteria that deserve special mention are N. gonorrhea and P. aeruginosa. Pseudomonas conjunctivitis is associated with contact lens use, and requires a different antibiotic selection. N. gonorrhea is a sight-threatening infection associated with globe perforation. (Am J Opthal 1986;102:575.) The eye will be very infected and chemotic with a thick discharge that reaccumulates quickly. There are often enlarged pre-auricular nodes (unusual for bacterial infections). If this is suspected, cultures of the discharge, IM ceftriaxone, topical antibiotics, and a referral to an ophthalmologist are indicated.
Not prescribing topical anitbiotics will probably be a tough sell to patients because they have traditionally been used
Chlamydia trachomatis, another cause of conjunctivitis, is one of the leading causes of blindness in developing countries, causing approximately 2.2 million cases of blindness in Africa. (Br J Ophthalmol 2001;85:897.) Although the majority of patients with this infection have genitourinary symptoms, some do not. Patients will complain of redness, photophobia, and foreign body sensation. There will be a fair amount of discharge. This type of conjunctivitis should be suspected in patients with GU symptoms or treatment failures for bacterial infections. Traditional culture methods do not grow this organism; one must use DFA or a PCR. The treatment is three weeks of doxycycline or a single 1 g dose of azithromycin.
Because differentiating between viral and non-gonococcal bacterial conjunctivitis is difficult and requires cultures (which, of course, are of little use at the time of presentation), who does one treat with antibiotics, and does anyone, excluding those with gonococcal or chlamydial conjunctivitis, need treatment? Certainly, viral (non-herpetic) conjunctivitis requires no specific treatment, and the supportive treatment recommendations of cool compresses and handwashing is all we should prescribe.
What if we misdiagnose a bacterial infection as viral? How will the patient do? A Cochrane Library review of three studies of 527 patients found 64 percent of patients with bacterial conjunctivitis treated with placebo were cured by days 2 to 5. (The Cochrane Library 2002, Issue 3, Oxford, UK.)
Treatment with antibiotics in bacterial disease did demonstrate an earlier cure, and the incidence of serious sequelae (orbital cellulitis, bacterial keratitis) in placebo and treatment groups was very low. The bottom line here is that there was weak evidence supporting the use of antibiotics (earlier cure), but not treating with antibiotics does not result in a poor outcome, and there is no chance of complications from antibiotic use (allergic and resistance issues).
Finally, which antibiotic should be used and for how long should we treat a presumed bacterial (non-gonnococcal, non-chlamydial) conjunctivitis, either secondary to strong clinical suspicion or parental/patient pressure? Suitable choices include trimethoprim-polymyxin B solution (Polytrim) or bacitracin-polymyxin B ointment (Polysporin) for seven days. I would suggest the solution for adults, ointment for children. Sodium sulfacetamide (Bleph-10), although once a very common choice, does not cover staphylococcus, Neisseria, or Serratia marcescens. (Ann Emerg Med 2002;40:524.)
Another commonly used antibiotic to be avoided is erythromycin, which like its oral/parenteral form has high levels of resistance in Streptococcus, Staphylococcus, and H. influenzae. (Principles and Practice of Infectious Disease. Ed. 2000:1251.) The quinolone and aminoglycoside antibiotics should be reserved for conjunctivitis associated with contact lens use due to the high incidence of Pseudomonas.
A few final thoughts: Topical anesthetics should never be given to the patient (they may lead to corneal scarring), nor should topical steroids (they may possibly exacerbate herpetic conjunctivitis), and the patient should avoid communal activities for 10 to 14 days or when the discharge disappears, whichever comes first. Lastly, not using topical antibiotics will probably be a tough sell to patients because they traditionally have been used in all cases, and if we don't, their family doctor probably will. So until there are very clear guidelines coming from large, well-designed studies, many patients with viral conjunctivitis will be leaving the ED or their doctor's office with a prescription for antibiotics.