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Assessing the Risk of Creutzfeldt-Jakob Disease
By Lawrence F. Muscarella, Ph.D.
Severalrecent reports have highlighted confusion, fear, and frustration over thepossible transmission of Creutzfeldt-Jakob disease (CJD) during surgery. Theethical, legal, and financial challenges faced by the prospect of a CJD outbreakare unfamiliar, formidable, and limited in precedence.
Each of these cases is strikingly similar. A hospital performs neurosurgeryon a patient not known at the time to have CJD. As many as several months later,this patient dies and during a postmortem brain biopsy is identified to have CJD.Because they are expensive and not disposable, the same set of instruments usedon this CJD-infected "index" patient is reprocessed and reusedmultiple times on several other patients. On news of the autopsy report andfearing a CJD outbreak, the hospital immediately quarantines or destroys itspotentially contaminated instrument set(s). Hospital administrators convene andseek counsel from ethicists, risk managers, and legal experts to determine anappropriate course of action. This process takes several weeks if not months,further delaying notification of each potentially CJD-infected patient. Whetherthe set of neurosurgical instruments was contaminated with prions during surgeryon the CJD-infected patient; remained contaminated after standard reprocessing(cleaning and sterilization); and infected several other subsequent patients isunknown and virtually impossible to determine.
Althoughthe risk of CJD infection from a contaminated surgical instrument is extremelyremote, the lack of a reliable and effective screening method for patientsinfected with CJD fuels many of the fears of a outbreak. As a result, the typesof cases described above are becoming all too frequent and familiar. Screeningtests similar to those used for HIV, hepatitis B, and hepatitis C have not yetbeen developed for CJD. In general, definitive CJD diagnosis currently requiresa postmortem brain biopsy. Adding to the frustration of this disease'sprognosis, which is always fatal, is the lack of a well-defined protocol foraddressing and resolving a potential CJD outbreak. The extremely low-risk of CJDtransmission during surgery ironically further complicates outbreakinvestigations, as arguments that it is unnecessary to notify patients of a riskthat is so remote may have some, albeit very little, credence.
What is CJD?
CJD is a fatal and rare neurological disease that affects approximately onein 1 million people per year worldwide1. Initial symptoms of CJD,whose incubation period can be decades long, include depression and poor memory,followed in its latter stages by dementia and loss of physical functioning. Insome cases, patients infected with CJD may not display symptoms for decades.Most cases of CJD occur sporadically1 although as many as 15% of allcases may be inherited.2,3 Less than 5% of all documented CJD casesresult from contact with contaminated surgical instruments. Currently there areno treatments for CJD.1
Prions, which are the infectious and rogue proteins believed to cause CJD,are unlike all other known pathogens. They do not contain genetic material anddisplay a remarkable and unique ability to survive routine cleaning and steamsterilization procedures. Prions are produced in cells through the processesknown as transcription and translation. Genes on a specific portion of a DNAmolecule ordinarily instruct the cell to synthesize "healthy"proteins. Cellular messengers attach to and transport amino acids (the buildingblocks of proteins) from the cell's cytoplasm to its ribosomes, where proteinsynthesis occurs. The retrieved amino acids are assembled into a specific orderdetermined by the genes' instructions. Like a chain-link fence, these aminoacids bond together to form a protein molecule. For unclear reasons, a mutatedor altered gene can cause the sequence of these assembled amino acids to becomeout of order,4,5 resulting in the production of infectious proteins,or prions.
Assessing the risk of prion infection during surgery
Algorithms designed to assess the risk of prion transmission are helpful, iflimited in their usefulness. Without a reliable screening method for CJD, takingprecautionary measures to avert CJD infection becomes problematic. Employing apolicy that assumes every patient is a CJD-carrier seems unrealistic. To beclear, the risk of being contaminated with prions during surgery is remote.According to the Centers for Disease Control and Prevention (CDC), no reports ofCJD transmission during surgery have been reported during the past 20 years.Further, only patients exposed to high-risk tissues, such as pituitary glandhormones, the brain's dura mater, spinal cord, cornea, and other types ofneurological tissues, are reported to be at risk for CJD.1 To date,CJD following endoscopy has not been reported.
What decontamination method effectively destroys prions?
Although extremely rare, reports of CJD infection linked to surgicalinstruments contaminated with prions have been published.1,6,7 Oddlyenough, standard sterilization processes, including heat, which are routinelyused to destroy all known microorganisms and viruses, may be ineffective againstprions1. And while cleaning likely reduces their numbers, it may notalways effectively remove all of the prions from a contaminated instrument1.Although some cleaning and sterilization methods are recommended for instrumentspotentially contaminated with prions, data demonstrating the effectiveness ofeach are limited.
The minimum requirements for decontaminating surgical instruments potentiallycontaminated with prions are unclear. Nevertheless, there are a few availableoptions that minimize, if not eliminate, the risk of CJD infection: 1,8,9
Each of these two steam sterilization cycles has been reported to be at leastsomewhat effective against prions. A process that includes cleaning theinstruments, exposing them to sodium hydroxide (1N, NaOH, or soda lye) or sodiumhypochlorite (NaOCl, or bleach) for 60 minutes, followed by a standard gravitysteam cycle, is also a possible option.1 Combining two or moredifferent procedures appears to be most effective.1,9 Incinerating,rather than reprocessing and reusing, reusable instruments should also beconsidered.
Toaid in assessing the potential risk of a surgical instrument transmitting prionsduring surgery, four scenarios are provided. The first presents the greatestrisk of CJD infection, the fourth the least risk. These scenarios, whichdescribe instruments that are either simple or complex in design andconstruction and tissues that are either low or high risk (e.g., the dura mater,cornea, and spinal cord), can be used as a basis to assess risk and to formulatean appropriate reprocessing procedure. Adapting these four scenarios to aspecific surgical setting, as well as creating others that may be moredescriptive and apt, may be necessary.
1. Complex instruments that are difficult to clean and sterilize and are incontact with high-risk neurological tissues: These instruments pose the highestrisk for transmitting prions. Only disposable instruments should be used. Ifreusable instruments are used, incinerating them immediately after use should beconsidered;
2. Simple instruments that are easy to clean and sterilize and are in contactwith high-risk neurological tissues: These instruments pose a risk for prioncontamination. The use of disposable instruments is recommended. If, however,their use is not feasible, obtaining from the reusable instruments'manufacturers sets of reprocessing instructions and data validating thateffective cleaning and sterilization of prions can be achieved without damagingthe instruments is recommended. Using an extended sterilization procedure aftereach use may be necessary (see above);
3. Complex instruments that are difficult to clean and sterilize and are incontact only with low-risk tissues: These instruments pose a negligible risk ofprion contamination. Nevertheless, because complex instrument designs canpreclude the removal and eradication of all types of microorganisms and virusesduring reprocessing, the use of disposable instruments is recommended.10If, however, their use is not feasible, obtaining from the reusable instruments'manufacturers sets of reprocessing instructions and data validating thateffective cleaning and sterilization can be achieved without damaging theinstrument is recommended. Using a normal sterilization cycle preceded bythorough cleaning will prevent nosocomial infection; and
4. Simple instruments that are easy to clean and sterilize and are in contactonly with low-risk tissues: For these types of instruments, there is virtuallyno risk of prion transmission. Using a normal a sterilization cycle preceded bythorough cleaning is sufficient and will prevent nosocomial infection.High-level disinfection may also be suitable.
These recommendations may be subject to change, as CJD and methods for thedestruction of prions become better understood.
Lawrence F. Muscarella, Ph.D. is the director of research and developmentchief for Custom Ultrasonics, Inc and infection control editor-in-chief of Q-NetMonthly.