Contact Lens Care & Compliance

Understanding MRSA Infections

By Susan J. Gromacki, OD, MS, FAAO

In the past four years since the Acanthamoeba and Fusarium keratitis outbreaks among contact lens wearers, much research has been performed regarding the etiology and pathogenesis of ocular infection (Gromacki 2010; Fleiszig 2010). However, since that time, eye infections caused by another pathogen, methicillin-resistant Staphylococcus aureus (MRSA), have been on the rise (Donnenfeld et al, 2010; Asbell et al, 2005).

Bausch + Lomb recognized this future trend in eye infection and utilized MRSA as a test organism for its new multipurpose solution, Biotrue. (This testing is not currently required by the U.S. Food and Drug Administration/International Standards Organization.) Biotrue achieved a 4.8 log reduction of MRSA strains following the recommended disinfecting time (soak only), exceeding the FDA/ISO 3.0 log reduction standard.

Unlike the more ubiquitous methicillin-sensitive Staphylococcus aureus strains, MRSA contains an enzyme that attacks the B-lactam ring of an antibiotic, rendering it resistant to penicillin, its synthetic derivatives (including methicillin), and the cephalosporins. It also demonstrates frequent resistance to the fluoroquinolones (ofloxacin, ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin), today's workhorses for ocular bacterial infection therapy. New fluoroquinolones, such as Besivance (besifloxacin, B+L), have yet to develop the resistance of the other medications in their group. In addition, this medication, along with Zymar (gatifloxacin, Allergan), contains benzalkonium chloride, which reportedly acts synergistically with the antibiotic to enhance the speed at which the bacteria are eradicated (Moshirfar et al, 2007).

MRSA Types and Treatment

Approximately 1.5 percent of the United States population is colonized with MRSA as part of its normal flora (Gorwitz et al, 2008; Kuehnert et al, 2006). There is little-to-no association between carrier status and infection, the latter of which is typically spread from skin-to-skin contact. As a result, incidence rates are highest in schools, dormitories, and military barracks; and in patients participating in high physical-contact sports or using locker rooms. This mode of transmission describes community-acquired (CA) MRSA. The other classification, hospital-acquired (HA, or nosocomial) MRSA, is found among hospital/healthcare employees/ patients and has the potential to be more virulent and resistant compared to its counterpart.

A MRSA skin infection typically manifests as pimples, abscesses, boils, or other puss-filled lesions. If untreated, MRSA can cause severe, sometimes fatal invasive disease (Klevens et al, 2007.) Typical therapy includes oral Bactrim (trimethoprim and sulfamethoxazole, 160mg/800mg) twice per day for 10 days, supplemented with topical Bactroban (mupirocin) for severe lesions. With early detection, treatment is generally successful on an outpatient basis.

MRSA eye infections can present as blepharoconjunctivitis, keratitis, cellulitis, dacryocystitis, or endophthalmitis. They are still rare enough that there is no established standard of care. Treatment depends on the location and severity of infection in combination with the individual patient's antibiotic sensitivity profile; typically, it includes oral and/or topical vancomycin and/or trimethoprim.

Stay Alert

In summary, clinicians need to be increasingly vigilant regarding MRSA as an etiology of eye infection, especially among patients unresponsive to conventional treatment. But we can be reassured that the latest generations of lens care systems and antibiotics do provide good coverage against this increasingly prevalent pathogen—at least for now. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #179.

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Dr. Gromacki is a Diplomate in the Cornea, Contact Lenses, and Refractive Technologies section of the American Academy of Optometry. She is chief research optometrist at Keller Community Hospital in West Point, N.Y.