This review sought to provide an overview of proposed methods and protocols for processing surgical instruments contaminated with prions. A search of PubMed was conducted to identify studies published between January 1, 2012, and January 2, 2019, with no language restrictions and using varying combinations of the following terms: prions (Medical Subject Heading [MeSH]) OR decontamination (MeSH) OR cleaning OR disinfection OR sterilization. Articles were excluded if they did not involve medical device surfaces or describe the processing protocol. At least two reviewers independently selected articles, extracted data, and assessed data. A total of 627 articles published in peer-reviewed journals were identified. Of the 55 articles assessed for full-text eligibility, eight met the inclusion criteria. Only a few studies investigated protocols and methods for processing prion-contaminated medical devices; therefore, determining the best way to sterilize device surfaces and preserve the integrity of surgical instruments remains challenging. Moreover, the perspective of sterile processing department staff continues to be overlooked when designing studies.
A prion or “proteinaceous infectious particle” is an infectious proteinaceous agent that causes transmissible spongiform encephalopathies (TSEs),1 –3 the most common form of which is sporadic Creutzfeldt-Jakob disease (CJD). CJD has a mortality rate of 1 to 1.5 cases per million each year worldwide.4 Although rare, the iatrogenic transmission of CJD has been reported previously in relation to the application of prion-contaminated human growth hormone, dura mater grafts, and corneal grafts.
However, few reports show the link between CJD-confirmed cases and prion-contaminated surgical instruments.4 A 23-year-old female patient and a 17-year-old male patient underwent stereo-electroencephalography using the same electrodes that were used previously for another patient who had a confirmed diagnosis of CJD. Consequently, the two patients died of CJD.5 The electrodes used for stereo-encephalography were cleaned with benzene and disinfected with 70% ethanol, then stored for two months in a metal box containing 2 g paraformaldehyde. Later, they were applied during a neurological procedure on a chimpanzee that expired after being infected with CJD.6 A decade later, a 46-year-old male patient died from confirmed CJD following cranial surgery in the same hospital where a female patient had died of confirmed CJD.7 Another report described cases of mortality following brain surgery, with one death occurring following the removal of two teeth.8 However, none of these reports could associate the cases of death with the contamination of surgical instruments. Therefore, these reports remain inconclusive.
The high resistance of prions to classic chemical and physical decontamination treatments is well known.9, 10 Inconsistency in eliminating prions from device surfaces, even following the recommended use of extended steam exposure, also has been reported.11 Instruments that contact high-risk tissue require adequate prion decontamination (using strong alkaline solutions or highly concentrated sodium hypochlorite) to reduce the risk to patients who are subsequently treated with these instruments.12, 13 However, these decontamination protocols can damage device surfaces14 ; therefore, a substantial number of novel disinfectants and processing protocols have been tested and studied to eliminate the risk of CJD transmission via surgical instruments.
This review sought to provide an overview of methods and protocols for processing surgical instruments contaminated with prions in reports published during a seven-year period.
This systematic review of the scientific literature was conducted to assess procedures for eliminating prions from the surfaces of surgical instruments. A PubMed search was performed to identify articles published between January 1, 2012, and January 2, 2019, on processing prion-contaminated medical devices. Different combinations of the following terms were used in the literature search: prions (Medical Subject Heading [MeSH]) OR decontamination (MeSH) OR cleaning OR disinfection OR sterilization. We did not apply language restrictions on the search (Figure 1).
One author (C.Q.M.B.) screened article titles and abstracts and excluded irrelevant search items. Then, the remaining titles with abstracts were screened for eligibility by two authors independently (C.Q.M.B. and R.Q.S.). Next, these two authors independently screened full-text articles and extracted data (e.g., citation, device surface used, type and amount of inoculum, processing methods used, outcome). Disagreements were resolved through consensus-based discussion between the reviewers. Articles were excluded if they did not involve device surfaces or if the processing protocol was not described.
In the initial search, 627 articles published in peer-reviewed journals during 2012–19 were identified (Figure 1). Of the 55 articles assessed for full-text eligibility, eight met the inclusion criteria and 47 were excluded because the study (1) involved biological surfaces, such as cells, rather than device surfaces or (2) did not describe the processing protocol. The results of the identified processing protocols used for decontamination of prion-contaminated device surfaces and their outcomes are described in Table 1.
To the authors' knowledge, no previously published review has assessed the processing of prion-contaminated surgical instruments. The results of the current review suggested that because the number of studies on processing methods of prion-contaminated instruments is small, leading practices for completely eliminating prions from surfaces and preserving the integrity of surgical instruments cannot be determined. Studies have focused on using materials other than stainless steel as the outer surface material of surgical instruments. Reports have shown that in the precleaning step, chemicals with known risks to the longevity of surgical instruments were used. These studies were associated with various shortcomings, including being written solely from the laboratory viewpoint and not considering the perspective of sterile processing department (SPD) staff. The lack of a practice-based perspective can lead to limitations in the application of the results. Further, because they involve safety risks for SPD staff, complicated processes should not be considered for implementation.
Considering that prions can resist steam sterilization processes (thermostability)15, 16 and prions' affinity for binding with metals, developing the cleaning phase of processing for thermoresistant and thermosensitive medical devices is critical. However, only one study has evaluated the cleaning phase adequately and showed positive results with the application of alkaline detergents, which are used by SPDs.11 Older studies demonstrated up to 99% reduction of organic and inorganic residues through the manual or automated cleaning of medical devices.17, 18 Presoaking and ultrasonic cleaners are recommended for use by SPDs,12 but their ability to eliminate prions has not been evaluated.
Studies that have proposed introducing new equipment and alkaline, acid, or chlorine solutions in SPDs19, 20 should consider the development of adequate standard operating procedures (SOPs) and management of solutions (i.e., storage and disposal) and equipment (i.e., qualification and validation), which require activity indicators and involve increases in costs and staff training. Also, processing time must be taken into consideration when proposing a processing protocol, in order to ensure viable practices.
The use of 1 nmol sodium hydroxide (NaOH) effectively eliminated prions from surgical instruments.21, 22 However, additional safety precautions need to be implemented in the SPD regarding use of NaOH, which could lead to irreparable damage of surgical instruments.14 Studies described the incidence of spills, corrosion, and, in one case, an explosion in the autoclave when 1 nmol NaOH was used.13
Various strains of TSEs were used (scrapie, ME7, 263K, and CJD), thereby reflecting the absence of standardized methods to investigate prion contamination. The lack of standardized methods also is a constraint to comparing results, as both prion strains and prion-contaminated devices can differ in several aspects.10, 23 Therefore, standardizing processing methods for medical devices, equipment qualification protocols, cleaning validation protocols, and protocols for monitoring cleaning methods is important.
Identifying prion-positive patients before surgical instruments are reused also is vitally important,22 especially because rapid assays that can detect prions in surgical instruments are unavailable in clinical settings. Until they become available, protein detection assays are viable alternatives for use in SPDs,24 though definitive evidence of the absence of protein and risk of prion transmission will remain absent.
Currently, a biopsy is not indicated for diagnosing patients for prion disease25 ; therefore, each healthcare facility should determine the practical situations when the SPD could receive a prion-contaminated surgical instrument. We cannot determine the exact situations when a patient with progressive dementia would undergo a surgical procedure, but an SOP still needs to be prepared in consideration of asymptomatic patients.
Another finding from the current review was the use of low-complexity samples (e.g., wires, tokens) that do not represent the complex instruments used in surgical practice, especially neurosurgeries. For cleaning instruments that contain lumens or dead ends and run on electric power, special protocols and SOPs that include these features will be required.
The application of innovative coatings26, 27 appears promising; however, in addition to being expensive alternatives, these coatings do not solve the problems associated with instruments currently used in SPDs. Moreover, these types of metal-coated instruments are not available for use in SPDs as of yet. Although keeping instruments moist28 is an inexpensive and easy alternative to reducing prion adsorption, biofilm formation is a concern.29, 30
The studies reported in this review did not adequately consider current processing practices when developing cleaning procedures for prion-contaminated surgical instruments. Inconsistencies in processing protocols, lack of standards regarding testing and testing end points, and variable results indicate that detailed research is needed to determine leading practices for cleaning and disinfecting prion-contaminated instruments.
The views, opinions, and/or findings contained herein are those of the authors and should not be construed to represent a position, policy, or decision of the School of Nursing at the University of São Paulo unless so designated by other documentation.
Camila Q.M. Bruna, PhD, RN, is a postdoctoral fellow in the School of Nursing at the University of São Paulo in São Paulo, Brazil. Email: firstname.lastname@example.org
Rafael Queiroz de Souza, PhD, RN, is a professor at Anhanguera University in São Paulo, Brazil. Email:email@example.com
Kazuko U. Graziano, PhD, RN, is a senior professor in the School of Nursing at the University of São Paulo in São Paulo, Brazil. Email: firstname.lastname@example.org