Invasive methicillin-resistant staphylococcus aureus (MRSA) infection ranks among the leading causes of death in the US. Reports on the incidence vary, but across the board it is common knowledge that the numbers are growing and fear exists that MRSA will one day soon outnumber methicillin-sensitive staphylococcus aureus (MSSA).
Reports on the demographics are not completely consistent. MRSA infections vary geographically. This may have something to do with the differences in healthcare structure by area. Studies report an equal incidence between men and women.
One of the main risk factors is age. Long-term use of antibiotics, with or without steroids, and hospitalization are all risk factors as well. But patients without exposure to health care environments are thought to be just as likely to be colonized with MRSA as health care workers.
When it comes to the eye, between 2000 and 2005, there was a greater than 10% rise in the prevalence of MRSA in ocular infections (from 29% to 41%). More recent studies show that out of s. aureus ocular infections, MRSA makes up more than half.
Conditions such as dry eye and immunosuppressive disorders are risk factors. Patients who have undergone keratoplasty also are more susceptible. MRSA has been linked to chronic dacryocystitis, even congenital nasolacrimal duct obstruction. This infection also can come from bacteremia and spread to the eye. Conjunctivitis is the most common type of ocular infection, followed by keratitis after corneal procedures, such as cross linking, and orbital cellulitis. As far as the orbit is concerned, Mathias et al. noted that MRSA infections of the orbit may have an atypical presentation, with lid swelling, lacrimal gland involvement, multiple orbital abscesses, and lack of an upper respiratory illness, paranasal sinus infection or trauma. Acute endophthalmitis, a potentially devastating disease resulting in poor visual outcome, also is often caused by MRSA.
MRSA infections can be classified as hospital acquired (HA) or community acquired (CA). Eyelid and lacrimal disorders tend to be more common in CA MRSA, whereas keratitis, endophthalmitis and wound infection are more common in HA MRSA. In general, HA MRSA infections are more resistant to antibiotics than CA MRSA. CA MRSA tends also to be more sensitive to Bactrim than HA MRSA.
Regardless of whether the bacteria is HA or CA, the bacterial isolates are usually multi-drug resistant, including resistance to many fluoroquinolones. It has been shown that fourth generation fluoroquinolones are effective, especially in community-acquired MRSA.
It has been reported that approximately 35% of staphylococcus aureus infections of the eye are methicillin-resistant. These isolates have shown high rates of multiple mutations and resistance to fluoroquinolones. Suzuki found that a compound called targocil functioned as a bacteriostatic inhibitor of bacterial wall techoic acid biosynthesis in s. aureus, a key role in the pathogenesis of eye infection.
Lefevre et al. studied the effectiveness of daptomycin in a rabbit model of MRSA endophthalmitis and found that 1 mg of intravitreal daptomycin was not inferior to 1 mg of intravitreal vancomycin, so this antibiotic could be considered for treatment.
Pelletier et al. found that povidone-iodine 0.4% mixed with dexamethasone 0.1% killed MRSA isolates within 15 seconds of exposure. This can be considered in high-risk patients.
Physicians choose different antibiotics to treat MRSA. But the bottom line is there are a few treatment options: trimethoprim-sulfamethoxazole, clindamycin, rifampin, gentamycin, chloramphenicol or vancomycin. Some patients will require hospitalization for IV antibiotics, some will require a minor procedure, such as debridement of necrotic tissues and some will require invasive procedures. Outcomes when MRSA involves the eye varies between good visual outcome to no light perception.
Nowadays, most ophthalmic surgeons pre- and post-treat their surgical patients with broad-spectrum antibiotics, and in this way probably avoid many cases of MRSA. Advances in the way we treat patients in hopes of prevention should decrease the incidence of MRSA in the ophthalmic population.
What we need to consider now is the threat of vancomycin-resistant strains. Unnecessary antibiotic use must be limited, especially in viral conjunctivitis, as this overuse contributes to resistance. Needless to say, MRSA is a growing public health problem that presents a treatment challenge for physicians. As ophthalmologists, we must be aware of appropriate practices to avoid this infection, but also be knowledgeable of ways to treat if necessary.