Charles G. Roberts

Inactivation of Animal and Human Prions by Hydrogen Peroxide Gas Plasma Sterilization

Prions cause various transmissible spongiform encephalopathies. They are highly resistant to the chemical and physical decontamination and sterilization procedures routinely used in healthcare facilities. The decontamination procedures recommended for the inactivation of prions are often incompatible with the materials used in medical devices. In this study, we evaluated the use of low-temperature hydrogen peroxide gas plasma sterilization systems and other instrument-processing procedures for inactivating human and animal prions. We provide new data concerning the efficacy of hydrogen peroxide against prions from in vitro or in vivo tests, focusing on the following: the efficiency of hydrogen peroxide sterilization and possible interactions with enzymatic or alkaline detergents, differences in the efficiency of this treatment against different prion strains, and the influence of contaminating lipids. We found that gaseous hydrogen peroxide decreased the infectivity of prions and/or the level of the protease-resistant form of the prion protein on different surface materials. However, the efficiency of this treatment depended strongly on the concentration of hydrogen peroxide and the delivery system used in medical devices, because these effects were more pronounced for the new generation of Sterrad technology. The Sterrad NX sterilizer is 100% efficient (0% transmission and no protease-resistant form of the prion protein signal detected on the surface of the material for the mouse-adapted bovine spongiform encephalopathy 6PB1 strain and a variant Creutzfeldt-Jakob disease strain). Thus, gaseous or vaporized hydrogen peroxide efficiently inactivates prions on the surfaces of medical devices.

Inactivation of human immunodeficiency virus type 1, hepatitis A virus, respiratory syncytial virus, vaccinia virus, herpes simplex virus type 1, and poliovirus type 2 by hydrogen peroxide gas plasma sterilization

BACKGROUND Studies were conducted to determine the capability of a hydrogen peroxide gas plasma sterilization process to inactivate several types of viruses. Six test agents were used: HIV type 1, human hepatitis A virus, respiratory syncytial virus, vaccinia, herpes simplex virus type 1, and poliovirus type 2. METHODS The test viruses were suspended in cell culture medium and dried on the bottom of sterile glass petri dishes. The inoculated dishes were processed in the hydrogen peroxide gas plasma system for half the normal sterilization cycle time. Four inoculated carriers for each virus were used in two separate half cycles. Infectivity of the test viruses and cytotoxicity to the indicator cell lines were assayed. RESULTS The hydrogen peroxide gas plasma sterilization process produced inactivation of the six viral test agents under these experimental conditions. The reduction in viral titers ranged from 2.5 log10 to 5.5 log10, a 99.68% to 99.999% decrease. CONCLUSIONS These results clearly demonstrate the virucidal effectiveness of the hydrogen peroxide gas plasma sterilization process against both lipid and nonlipid viruses.

The role of biofilms in reprocessing medical devices

Biofilms are communities of microorganisms within extracellular polymeric material attached to surfaces. Within a biofilm, cells have some protection from drying and other stress factors in their environment, including antimicrobial agents. In this article, the challenges to medical device reprocessing posed by biofilms are addressed. Biofilm formation on reusable medical device surfaces is a risk that can be controlled. By ensuring prompt device cleaning and reprocessing either by high-level disinfection or sterilization and proper drying, biofilms will not have a chance to form. Reusable medical devices like flexible endoscopes that are promptly cleaned and disinfected, rinsed and dried pose little risk to patients.

Virucidal activity of ortho-phthalaldehyde solutions against hepatitis B and C viruses

Ortho-phthalaldehyde (OPA), a high-level disinfectant alternative to glutaraldehyde, was tested for efficacy against human hepatitis B virus (HBV) and hepatitis C virus (HCV) using surrogate animal viruses. HBV and HCV are the most prevalent human bloodborne viruses but have not yet been propagated in the laboratory. The surrogate viruses, duck hepatitis B virus (DHBV) and bovine viral diarrhea virus (BVDV), were used to assess the virucidal efficacy of OPA on HBV and HCV, respectively. After a timed exposure to the test disinfectant, the surrogate virus dried on a hard surface was neutralized and assayed to detect viable viruses using appropriate cell lines. A greater than 4-log(10) reduction in virus titer was demonstrated using dilute OPA solutions against dried DHBV and BVDV after 5 minutes of exposure at 20 degrees C. OPA was shown to be efficacious against surrogate viruses for human hepatitis B and hepatitis C virus. This is the first time that OPA efficacy has been demonstrated for HBV and HCV.

Sterilization of a small caliber vascular graft with a polyexpoxy compound

Sterilization of tissue based medical devices via cold sterilization processes has been limited to formaldehyde, glutaraldehyde, and mixtures of the same with alcohols and surfactants. The authors report the sterilization of a small caliber vascular graft with a combination of diglycidyl ether and ethanol. The sterilant contains 1–4% diglycidyl ether and 10–20% ethanol as an aqueous solution. Sterilization is achieved after exposure of the graft to the sterilant solution for a period of 7 days at an elevated temperature (30°–40° C). The biologic indicator selected for efficacy studies was Bacillus subtilis niger ATCC 9372 (endospores). The grafts were inoculated with a concentrated endospore suspension and immersed in the sterilant solution for increasing time periods. After extensive rinsing over membrane filters to remove any residual sterilant, the grafts and filters were cultured in tryptic soy broth. D10 values were calculated using a fraction-negative, most probable number technique. Additionally, many representative bacteria and fungi were tested and found to be susceptible to the new sterilant developed. The diglycidyl ether/alcohol sterilant developed was found to be efficacious for sterilization of the tissue based vascular grafts tested.

Hydrogen Peroxide Vapor and Aerosol Room Decontamination Systems

To the Editor—We read with great interest the recent article by Holmdahl et al, 1 “A Head-to-Head Comparison of Hydrogen Peroxide Vapor and Aerosol Room Decontamination Systems,” which compared 2 distinctly different hydrogen peroxide vapor systems. The study, as designed, was well executed and obtained results that could be expected on the basis of the methodology employed. We would like to point out to readers and to the study authors some points of methodology that we do not believe are appropriate for this type of study. There is a basic study assumption that a 6-log kill of spores is the appropriate target for room decontamination. A 6-log kill is definitely appropriate for terminal sterilization of critical medical devices if the devices are used in normally sterile body sites. 2 The goal of room decontamination is significantly different: to eliminate potentially pathogenic microorganisms contaminating room surfaces. The Holmdahl et al 1 study used biological indicators with a 6-log concentration of Geobacillus spores in a Tyvek pouch. A packaged 6-log biological indicator configuration is appropriate and commonly used for terminal sterilization, but it is not consistent with the goal of room decontamination and presents an unduly high level of challenge. It is our opinion that employing the requirements for terminal sterilization is not appropriate and does not serve the user community well. Literature and surface sampling performed in hospital rooms with contact plates or swab samples has revealed that real-life contamination of hospital room surfaces after cleaning rarely exceeds a 2-log concentration. 3 Overcoming an unreasonably high challenge (a 6-log concentration of Geobacillus spores in a Tyvek pouch) requires a higher than necessary dose and concentration of hydrogen peroxide. Higher doses and concentrations of hydrogen peroxide increase the impact to the environment, compared with that of a process that uses a lower concentration and dose of the same active ingredient. The Glosair System (formerly Sterinis) uses a 5%–6% concentration of peroxide to reduce the environmental risk yet achieves kill levels consistent with known hospital room bioburden levels. We would be glad to work with the study authors to repeat their testing under conditions more representative of real-world conditions.