Prion inactivation and medical instrument reprocessing: challenges facing healthcare facilities.

Abstract

The major transmissible spongiform encephalopathies (TSEs) of humans include Creutzfeldt–Jakob disease (CJD), kuru, fatal familial insomnia, Gerstmann– Straussler–Scheinker syndrome, and, within the past 10 years, variant CJD (vCJD).1-3 The pathology of these neurodegenerative diseases of the central nervous system is associated with the presence of pathologic prions, an abnormal conformation of a normal cellular protein.4 Fomites and tissues contaminated with prions, such as dura mater and corneas, can transmit disease to humans.5 At least six cases of CJD have been attributed to the use of neurosurgical instruments and depth electrodes contaminated with prion-containing neural tissues.6 These cases of device-associated transmission highlight the challenges and data gaps that confront healthcare staff responsible for disinfection and sterilization of hospital equipment. The work described by Yan et al.7 in the lead article of this issue of Infection Control and Hospital Epidemiology represents an attempt to address the gap in our knowledge regarding prion decontamination and low-temperature sterilization methods. Pioneering research conducted at the National Institutes of Health in the early to mid-1980s provided evidence that prion proteins demonstrated significant resistance to conventional sterilization and disinfection methods.8,9 A recent review by Taylor10 reveals the complexity of prion inactivation. Most of the reported studies focused on prion inactivation in tissues. A remaining question is, how applicable is this research to surgical instrument reprocessing? Can laboratory-based inactivation methods be applied to central sterilization department operations? Three major conclusions can follow from review of the literature. First, prion inactivation research was not designed to assess instrument reprocessing strategies until only recently. Most prior research had focused on inactivating prions present in small amounts of whole brain tissue or neural tissue homogenates. It is only the more recent work that has studied prion inactivation on surfaces. If this contaminated neural tissue is present on surfaces (eg, neurosurgical instruments), a high prion burden embedded in organic material would pose a significant challenge to any inactivation method. Cleaning the surface to remove gross tissue should reduce the prion burden.11,12 Recent research showing that prions bind tightly to steel underscores this importance of cleaning to remove tissue.13,14 If prion-containing material is dried or heat-fixed onto surfaces, unusually thermostable subpopulations of prions remain even after autoclaving; animal assays have shown that infectivity persists.15 These studies indicate that instruments contaminated with prion material should not be allowed to dry prior to a thorough cleaning or decontamination process. Second, most research has used experimental designs that do not resemble contemporary commercial or routine practices of medical instrument reprocessing in healthcare. Prion inactivation data suggest that a more rigorous approach is needed. Research in laboratories around the world has shown that adding a chemical hydrolysis step (eg, use of sodium hydroxide [NaOH]) into prion inactivation strategies is a relatively effective means of reducing prion titers in neural tissue as demonstrated in animal assay experiments.16 Combining the use of NaOH as an instrument immersion step with autoclaving in a gravitydisplacement sterilizer was deemed a particularly effective strategy for prion inactivation.17 This approach, however,