Atypical mycobacteria drop, while gram-positive organisms rise

June 15, 2005

Washington, DC—Results of the 2004 American Society of Cataract and Refractive Surgery (ASCRS) survey of infectious keratitis after refractive surgery show there has been an end to the epidemic of atypical mycobacterial infections.

Nevertheless, the incidence of infectious keratitis has risen since last studied in 2001, and that phenomenon reflects a rise in infections caused by gram-positive organisms, said Eric D. Donnenfeld, MD, at World Cornea Congress V.

"There has been a dramatic decrease in the incidence of atypical mycobacterial infections, presumably secondary to the introduction of fourth-generation fluoroquinolones, and probably also due to improvements in sterile technique," said Dr. Donnenfeld, assistant clinical professor of ophthalmology, New York University Medical Center, New York. "Meanwhile, there has been an increase in gram-positive infections that most likely involve resistant organisms such as methicillin-resistant Staphylococcus aureus (MRSA)."

In 2001, 116 post-LASIK infections were reported by 56 surgeons. Based on their report of performing 338,500 procedures, those data translated into a rate of one case of infectious keratitis per 2,919 cases. In the 2004 survey, 48 cases of infectious keratitis were reported (39 LASIK, nine surface ablation) by 46 surgeons performing an estimated 102,300 procedures, representing a rate of one case of infectious keratitis per 2,131 procedures.

Analyses of causative pathogens revealed that atypical mycobacteria accounted for nearly half of the cases reported in 2001, whereas in the more recent survey, it was responsible for only one in 20 infections.

"No patient who received a fourth-generation fluoroquinolone as prophylaxis has developed an atypical mycobacterial keratitis," Dr. Donnenfeld said. However, while Staphylococcus species accounted for 33% of cases in 2001, in 2004 it had become the predominant cause by far, accounting for 61% of the reported cases.

"Obtain a specimen for culture and do not rely on empiric therapy because the causative pathogens may be opportunistic organisms or MRSA that are not responsive to conventional antibiotics," he said.

In both surveys, presentation of the infection was usually early, although in some cases it was delayed as late as 1 month. A comparison between the two surveys showed the frequency of cases with a late presentation had decreased, which was consistent with the decrease in mycobacterial infections.

Evaluation, diagnostic trends According to the results of the 2001 survey, flap elevation and scraping the bed were performed in only 39% of cases in 2001, compared with 46% of cases in 2004. At the same time, however, while the majority of cases (59%) were diagnosed at initial pre-sentation in 2001, the majority of cases (65%) were not diagnosed at initial pre-sentation in 2004. There was little change in the rate of performance of flap removal-15% in 2001 versus 12.5% in 2004.

"Surgeons appear to be doing a better job in their work-up when infectious keratitis was suspected, although it seems that treatment continues to be delayed in an appreciable proportion of patients, probably due to lack of suspicion," Dr. Donnenfeld said.

Best-corrected visual acuity (BCVA) outcomes showed most patients returned to excellent vision after resolution of the infection in both study periods. However, the results were poor in several cases. Penetrating keratoplasty was required for 10 eyes in 2001 and for three eyes in 2004. A single eye underwent enucleation in the 2001 series, but that was not required in any case in 2004.