Infectious conjunctivitis, infectious keratitis remain challenging
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Ocular surface infections include infectious conjunctivitis and infectious keratitis.
Infectious conjunctivitis is much more common, with an estimated incidence of 3 million to 6 million cases per year in the U.S. Infectious keratitis is 100 times less common, with 30,000 to 75,000 cases a year, but more often sight threatening.
Most infectious conjunctivitis, 65% to 90%, is viral in origin, with the most common pathogen being adenovirus. The QuickVue adenoviral conjunctivitis test available from Quidel is a useful screening tool. Adenovirus conjunctivitis is extremely contagious, and caution is advised in seeing and treating these patients. Many eye clinics have a so-called “red eye room” where patients with possible infectious conjunctivitis are directed to avoid infecting staff or other patients.
There is no FDA-approved therapy for adenoviral conjunctivitis, and most cases are self-limited. Some have reported that a combination of 1% povidone-iodine in a BAK-preserved eye wash or artificial tears can be useful in reducing symptoms and shortening the duration of viral shedding. Zirgan (ganciclovir ophthalmic gel, Bausch + Lomb) off label has also been recommended by some. The subset of epidemic keratoconjunctivitis can be sight threatening with the development of visually significant subepithelial infiltrates. Many ophthalmologists have suffered from epidemic keratoconjunctivitis infections sustained in their practices.
Most of the remaining infectious conjunctivitis cases are bacterial in origin, and the most common pathogens are Staphylococcus aureus, Streptococcus pneumonia, coagulase-negative Staphylococcus, Haemophilus influenzae and the feared Pseudomonas aeruginosa. However, many other microbial species, including rarer bacteria, fungi, chlamydia and even Acanthamoeba, may be causative. Corneal ulcers are often bacterial in origin, but viral causes including herpes simplex and herpes zoster as well as the other microbes listed above are also common.
Many studies have shown that we ophthalmologists are poor at differentiating the pathogen in both infectious conjunctivitis and infectious keratitis. Because most infectious conjunctivitis cases are not sight threatening, empirical therapy is often employed without identifying the inciting pathogen. In the rarer infectious keratitis, especially if more central on the cornea, laboratory diagnosis is appropriate. Classically, we have relied on corneal scraping with placement of the specimen on glass slides for gram and Giemsa staining along with C-streak culturing on blood agar, chocolate agar and Sabouraud medium.
We now have another helpful diagnostic in HealthTrackRx and other PCR panels. I would encourage every ophthalmologist to become familiar with a PCR diagnostic panel, which can help identify rarer pathogens including fungi, Acanthamoeba and atypical herpes infections. A simple swab or scrapings placed on a swab can generate pathogen diagnosis in 24 hours with some antimicrobial sensitivity information. The Ocular Tracking Resistance in US Today (Ocular TRUST) and Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) studies confirm that antimicrobial resistance of all pathogens is increasing. Many staphylococci species are methicillin resistant, and in one series, 15% were also resistant to fluoroquinolones, a common antibiotic selected for initiation therapy.
This has motivated many corneal specialists who deal with the more sight-threatening corneal ulcers to initiate therapy with fortified combination antibiotics. A subsidiary of Harrow, ImprimisRx, recently made Fortisite, a compounded eye drop that contains 1.5% tobramycin and 5% vancomycin, available by physician prescription. Some doctors are keeping a bottle of Fortisite on hand in their clinics for initiation of therapy for sight-threatening infections.
Infectious conjunctivitis and infectious keratitis remain a common challenge for the eye care professional. Greater use of PCR panels like those available from HealthTrackRx can provide more accurate and rapid diagnosis of the causative pathogen. While we have a broad array of commercialized antimicrobial agents, many infections today require the off-label use of currently approved drugs and/or the use of compounded eye drops for therapy. Unfortunately, the development and regulatory approval of new and better antimicrobial agents is not attracting significant investment as the return on investment is low.
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