Atypical microbacteria pose a risk for LASIK patients

Since they are serious infections with frequently poor outcomes, refractive surgeons and ophthalmologists should know how to identify them, continued Dr. Mah, who explained how he handles these patients to colleagues at the Current Concepts in Ophthalmology meeting, sponsored by Johns Hopkins University School of Medicine, Baltimore, and Ophthalmology Times.

Unfortunately, atypical microbacterial infections are increasing in frequency, likely because of an altered host defense with deep inoculation. Five cases of bilateral microbacterial infections after LASIK have been reported. Treatment may require amputation of the flap or lengthy antibiotic therapy. The differential diagnosis should include epithelial ingrowth or downgrowth, infections with various microorganisms, and diffuse lamellar keratitis (DLK), according to Dr. Mah, who is assistant professor of ophthalmology, Cornea, External Disease and Refractive Surgery Service, University of Pittsburgh School of Medicine, Pittsburgh.

"There is a bimodal occurrence: in infections that occur early postoperatively, the typical gram-positive pathogens are found, and in later infections the atypical microbacteria are the primary agents. The sources of pathogens may be the patient, intraoperative conditions, or the surgeon. Many infections that develop as a result of the surgery occur because there is no standard protocol for the laser centers to follow," he explained.

Importantly, at least half of the infections reported in the literature are the result of probable contamination with atypical microbacteria.

"This is a huge phenomenon that is occurring because of LASIK," Dr. Mah stated. The microbacteria are everywhere and in one study 16% of the eye wash stations in one eye center were found to be contaminated with atypical mycobacteria.

Prevention is key Several studies have investigated ways to prevent infections with atypical microbacteria. The newer fourth-generation fluoroquinolones, moxifloxacin 0.5% (Vigamox, Alcon Laboratories) and gatifloxacin 0.3% (Zymar, Allergan), were reported to be broad-spectrum agents that can eradicate atypical microbacteria. Levofloxacin 1.5% (Iquix, Santen, Vistakon Pharmaceuticals) also is effective but not to the same extent that moxifloxacin and gatifloxacin are. Clarithromycin (Biaxin, Abbott Laboratories) covers Mycobacterium chelonae, but the minimal inhibitory concentration of amikacin (Amikin, Bristol-Myers Squibb) is not comparable to those of the fluoroquinolones or clarithromycin, according to Dr. Mah.

A study of keratitis isolates that Dr. Mah and his colleagues completed, and published, replicated the results of previous studies and showed that moxifloxacin and gatifloxacin performed better than other antibiotic choices.

"Considering the choice of a prophylactic drug, it is important to choose one that covers the microorganisms of concern," he said.

A toxicity study performed by Daniel S. Durrie, MD, showed that moxifloxacin and gatifloxacin were well tolerated in patients who had undergone LASIK.

Dr. Mah pointed out that cases of microbacterial infection can be confused with DLK. However, differentiating between the two is important because the treatments are not the same.

"With mycobacterial infections, treat topically and orally. Administer a fourth-generation fluoroquinolone as well as other agents. We use topical clarithromycin or topical azithromycin (Zithromax, Pfizer/ Roerig)," Dr. Mah explained. "We also use topical amikacin. It is essential to stop steroids, which will worsen the infection. Clinically, the patient will get worse before improvement is seen. These infections often occur in clusters, so all the patients treated during the same period should be examined to rule out a similar infection."