Recurrent DLK outbreaks call for strict cleaning protocols

San Diego-Recurrent outbreaks of diffuse lamellar keratitis (DLK) seem to be associated with problems with cleaning protocols and bacterial contamination. Constant vigilance and maintenance of strict cleaning protocols are essential to prevent recurrences of DLK, said Simon P. Holland, MD.

An outbreak of DLK is defined by the Centers for Disease Control in Vancouver, British Columbia, where Dr. Holland is clinical professor, department of ophthalmology, University of British Columbia, as two or more patients presenting with DLK within a 3-day period.

The endotoxin theory During the initial outbreak in his department, Dr. Holland and his colleagues developed what he called "an endotoxin theory," because the only effective approach was sterilizer cleaning, which was associated with a decrease in DLK. The investigators theorized that endotoxins from bacterial biofilms in the sterilizer reservoir might have caused the outbreak. Such endotoxins are not destroyed by short-cycle, steam sterilization, which is used in most laser refractive clinics.

In a prospective, controlled study, Dr. Holland and colleagues investigated 55 outbreaks in 41 clinics on site when possible and developed basically three strategies to combat the outbreak: reviewing the environmental surgical process; looking at bacterial and biofilm contamination; and trying to determine incidence retrospectively related to changes made at each clinic to control the outbreak.

"The predominant bacteria found in clinics with DLK outbreaks are gram-negative (Pseudomonas). Interestingly, from a microbiological perspective, is the discovery of rare antibiotic-resistant bacteria such as Sphygmoma and Ralstonia, which have been isolated in cystic fibrosis," he said. The most frequent site of contamination was the internal reservoir of the sterilizer.

Of the 55 outbreaks, 41 were primary and came under control the first time an investigation was done into the cause. Over a 5-year period, 10 of the clinics had 14 recurrent outbreaks; four clinics had more than one recurrence. One intervention failed because of persistent outbreaks of DLK over 5 years, Dr. Holland reported.

Types of interventions The investigators used different types of interventions, including dry heat sterilization, modifications of the steam sterilization time (use of a dry heat sterilizer rather than short-cycle steam), use of disposable instruments, and use of enzymatic and biocide cleaning. Improvement of air quality was another approach; however, in some clinics that relocated, the DLK outbreaks still recurred.

"When we tried to determine the most important factors in the recurrent outbreaks in the 10 clinics, surprisingly we found that the same strain of bacteria had recontaminated sites in the surgical process that accessed the stromal bed," Dr. Holland said.

In one institution there had been a 22% incidence of DLK in the initial outbreak and the distilled water was found to be contaminated. There was a recurrence 1 year after the initial outbreak, and when Dr. Holland and colleagues evaluated the clinical site, they found that the distilled water supply was recontaminated. Four years after the initial recurrence, the third major DLK outbreak occurred and persisted despite numerous attempts to decontaminate the site and relocation of the clinic. The interior reservoir of the STATIM (SciCan) at the new site was found to be contaminated, and the outbreak was resolved by improved cleaning and sterilization.

"By cleaning the reservoir and keeping it dry, the number of bacteria that build up is limited," he said. "When the appropriate protocols were re-introduced, the problem resolved.