Last week, we learned that thirteen patients in New England - including five treated at Cape Cod Hospital - may have been exposed to the protein that causes Creutzfeldt-Jakob disease (CJD), a fatal brain disease similar to "mad cow."
At the root of the scare are reusable surgical instruments that were used on a patient later suspected to have the disease. To date, all reports have indicated that the equipment - a metal reference frame and brace - was properly sterilized, but that standard sterilization protocols don't necessarily eliminate CJD-causing proteins, known as prions.
Prions aren't just typical proteins. They're proteins that are normally produced by the body, but mis-folded versions that act like an infectious agent, inducing other copies of the protein to assume the mis-folded configuration.
I asked Dr. Deborah Yokoe, assistant professor of medicine at Harvard Medical School and Brigham and Women’s Hospital Epidemiologist,, to explain why prions might not be destroyed by standard sterilization. Dr. Yokoe's research focuses on tracking health-care related infections.
What is the standard protocol for sterilizing surgical instruments that are reused?
Because most surgical instruments come into contact with body tissues or fluids that are normally sterile, they are classified as “critical” items and must undergo both initial cleaning to remove blood, tissues, etc., then undergo sterilization. Sterilization is defined as a process that destroys all microorganisms, including spores. Sterilization can be achieved through heat sterilization (e.g., steam) or low-temperature sterilization techniques (e.g., ethylene oxide [“gas sterilization”], hydrogen peroxide gas plasma, periacetic acid sterilization). The choice of sterilization method usually depends on what is compatible with the particular piece of equipment. For example, some equipment cannot tolerate high temperatures. Regardless of the method used, strict parameters must be adhered to.
Why isn't this enough to destroy prions?
Prions are unusually resistant to conventional chemical and physical decontamination methods. This may be related to the fact that all of the other organisms contain nucleic acid (DNA or RNA) and are killed by sterilization processes that affect nucleic acid. Prions contain protein but lack nucleic acid (so are not technically “microorganisms”), so are quite unique.
Are there other disease-causing agents that are not addressed with standard sterilization?
All other disease-causing agents, including spores, are killed/destroyed by standard sterilization.
There are procedures that can address prion contamination. Why aren't these standardly employed in U.S. hospitals?
Some methods that have been shown to be effective against prions, such as immersion in sodium hydroxide, are very corrosive, or involve steam sterilization at much higher temperatures for longer time periods than is used for routine sterilization. There are many surgical instruments that aren’t able to tolerate these conditions. It’s also not practical to use only disposable instruments since disposable versions aren’t always available and when they are, may not have the same level of quality from the surgeons’ perspective as reusable equipment.
Some scientists think that prions may be involved in other neurodegenerative disorders, including Parkinson's and Alzheimer's. Should we be worried about the spread of these diseases via reused surgical equipment?
Although there are some similarities between these conditions, currently there’s no clear evidence that Alzheimer’s dementia or Parkinson’s disease is caused by prions or that either of these conditions can be transmitted from person-to-person or via reused surgical equipment.