Prion Sterilization: Common Challenges

Transmission of prion diseases through medical equipment remains an ever-present possibility in many laboratories and medical facilities around the world. As such, prion sterilization should not be taken lightly. Facilities that lack prion sterilization equipment and protocols for exposed or contaminated medical instruments not only put lab personnel at risk, but also endanger any future patients who may be treated with those instruments, even after they’ve been processed.

To understand the dangers of prion disease exposure, look no further than a 2013 case in which a New Hampshire hospital accidentally exposed eight patients to the infectious protein, which is known to damage the brain and leave it full of holes. The hospital in question used surgical instruments that had been previously used on a patient who later died from a particular prion disease.

This incident both underscores the importance of prion sterilization and highlights the challenges associated with it. In this article, we’ll discuss some of those challenges and offer insight on how to protect your laboratory personnel from prion diseases.

What Are Prions?

The Centers for Disease Control and Prevention (CDC) defines prions as “abnormal, pathogenic agents that are transmissible and are able to induce abnormal folding of specific normal cellular proteins called prion proteins that are found most abundantly in the brain.”

The Scientific American further describes a prion as “a term first used to describe the mysterious infectious agent responsible for several neurodegenerative diseases found in mammals” — diseases which include Creutzfeldt-Jakob disease (CJD) and Gerstmann-Straussler syndrome (GSS) in humans.

While CJD predominantly occurs due to sporadic transmission or heredity, iatrogenic transmission — that is, healthcare-associated transmission — of CDJ has been reported in over 500 patients. The CDC states that each of these “equipment-related cases occurred before the routine implementation of sterilization procedures currently used in health care facilities.”

While one might assume that current laboratory decontamination and sterilization protocols are sufficient to mitigate the threat of prion transmission, it isn’t that simple. To protect against prion diseases, laboratories need to implement dedicated prion sterilization protocols and procedures.

Prion Biosafety Requirements

When handling prions, it’s important for personnel to take the appropriate precautions in order to prevent cross-contamination and iatrogenic transmission. Facilities that handle prions are categorized as biosafety level 3 (BSL-3) laboratories and, as a result, are subject to the following requirements:

• All work must be strictly controlled and registered with the appropriate government agencies.
• Laboratory personnel are required to submit to medical surveillance and receive immunizations for the microbes they work with.
• Laboratory personnel must wear personal protective equipment, including solid-front wraparound gowns, scrub suits, or coveralls, gloves, and respirators.
• All procedures that can cause infection from aerosols or splashes must be performed within a biological safety cabinet.
• Laboratory personnel must have access to a hands-free sink and eyewash station, located near an available exit.
• A BSL-3 laboratory must be designed with sustained directional airflow to draw air into the laboratory from clean areas toward potentially contaminated areas.
• Exhaust air from a BSL-3 laboratory cannot be recirculated.
• Access to a BSL-3 laboratory must be restricted and controlled at all times.

The Problem with Prions

Compared to other pathogenic agents, prions are incredibly resistant to most routine methods of decontamination and sterilization. According to an article published in the Clinical Infectious Diseases journal, no single method of decontamination or sterilization has been shown to be 100% effective against prions. To that end, “a combination of methods has been recommended, including thorough cleaning, chemical treatment, and/or steam sterilization.”

The article further states that:

“Because CJD is not readily inactivated by conventional disinfection and sterilization procedures, and because of the invariably fatal outcome of CJD, the procedures for disinfection and sterilization of the CJD prion have been both conservative and controversial for many years.”

To make things even more challenging, there is no single definitive source on how to process medical equipment that has been exposed to prion disease. The World Health Organization (WHO), CDC, and the Association for the Advancement of Medical Instrumentation (AAMI) all provide different recommendations, some of which conflict with one another.

Additionally, some top agencies offer no guidance on how to process prion-contaminated medical instruments; for example, the U.S. Food and Drug Administration does not have an approved process for the prion sterilization of reusable surgical instruments.

Prion Sterilization with Autoclaves

Laboratories and healthcare facilities in the United States follow the AAMI’s national standards for disinfecting and sterilizing medical equipment that has come into contact with prions. These standards are approved by the American National Standards Institute (ANSI).

According to AAMI ST79, prions’ high resistance to standard sterilization methods requires special procedures for reprocessing medical instruments. The Guideline for Disinfection and Sterilization of Prion-Contaminated Medical Instruments, a whitepaper published by the Society of Healthcare Epidemiology of America that cites AAMI ST79, recommends the following:

• Instruments should be kept wet (e.g., immersed in water or a prionicidal detergent) or damp after use and until they are decontaminated, and they should be decontaminated (e.g., in an automated washer-disinfector) as soon as possible after use. Dried films of tissue are more resistant to prion inactivation by means of steam sterilization than are tissues that are kept moist.
• After the device is clean, it should be sterilized either steam sterilization with an autoclave, or a combination sodium hydroxide and autoclaving, using one of the four following methods:
  • Option 1. Autoclave at 134°C for 18 minutes in a prevacuum sterilizer.
  • Option 2. Autoclave at 132°C for 1 hour in a gravity displacement sterilizer.
  • Option 3. Immerse in 1 N NaOH (1 N NaOH is a solution of 40 g NaOH in 1 L water) for 1 hour; remove and rinse in water, then transfer to an open pan and autoclave (121°C gravity displacement sterilizer or 134°C porous prevacuum sterilizer) for 1 hour.
  • Option 4. Immerse in 1 N NaOH for 1 hour and heat in a gravity displacement sterilizer at 121°C for 30 minutes, then clean and subject to routine sterilization.

Healthcare facilities should tread carefully during prion sterilization, as it remains unclear which of the options listed above is best for completely eradicating prions from medical equipment. Please note that flash sterilization is not suitable for prion-contaminated devices.

Any prion-contaminated medical instruments in need of processing must be compatible with their intended sterilant, according to the AAMI. If the contaminated device cannot be cleaned or exposed to steam and other sterilants, the AAMI advises discarding that device.

Finally, the AAMI encourages all laboratories and medical facilities to establish a policy that focuses on disinfection and prion sterilization efficacy. This policy should prioritize the following:

• Sterilizer maintenance and repair history
• Sterilization process monitoring using physical, chemical, and biological monitors
• Disinfectant concentration

If you have additional questions about how to process prions or any other questions related to autoclaves in general, please contact us for more information.

Find the Right Autoclave for All of Your Sterilizing Needs

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1. Scientific American, “Surgical Exposure to a Brain-Eating Protein: A Small but Unavoidable Risk, https://www.scientificamerican.com/article/surgical-exposure-to-cjd-prion/.”
2. Centers for Disease Control and Prevention, “Prion Diseases, https://consteril.com/how-does-a-laboratory-autoclave-work/.”
3. Scientific American, “What Is a Prion?, https://www.scientificamerican.com/article/what-is-a-prion-specifica/.”
4. Centers for Disease Control and Prevention, “Creutzfeldt-Jakob Disease, Classic (CJD), https://www.cdc.gov/prions/cjd/index.html.”
5. National Institute of Neurological Disorders and Stroke, “Gerstmann-Straussler-Scheinker Disease, https://www.ninds.nih.gov/health-information/disorders/gerstmann-straussler-scheinker-disease.”
6. Centers for Disease Control and Prevention, “Infection Control | Creutzfeldt-Jakob Disease, Classic (CJD), https://www.cdc.gov/prions/cjd/infection-control.html.”
7. Consolidated Sterilizer Systems, “Do You Know the Difference Between Biosafety Levels 1, 2, 3 & 4?, https://consteril.com/biosafety-levels-difference/.”
8. Clinical Infectious Diseases, “The Challenge of Prion Decontamination, https://academic.oup.com/cid/article/36/9/1152/312297.”
9. AAMI, “ANSI/AAMI ST79, https://www.aami.org/standards/ansi-aami-st79.”
10. National Library of Medicine, “Guideline for disinfection and sterilization of prion-contaminated medical instruments, https://pubmed.ncbi.nlm.nih.gov/20055640/.”
11. National Library of Medicine, “Inactivation Methods for Prions, https://pubmed.ncbi.nlm.nih.gov/31507270/.”
12. Consolidated Sterilizer Systems, “Steam Sterilization Cycles, Part 1: Gravity vs. Vacuum, https://consteril.com/steam-sterilization-cycles-part-1-gravity-vs-vacuum/.”
13. Consolidated Sterilizer Systems, “Laboratory Autoclave Steam Sterilization Cycles, Part 10: Immediate-Use (Flash) Sterilization Cycle, https://consteril.com/immediate-use-flash-sterilization-cycle/.”