Prion diseases--an evidence-based protocol for infection control

A direct assessment of human prion adhered to steel wire using real-time quaking-induced conversion

Accidental transmission of prions during neurosurgery has been reported as a consequence of re-using contaminated surgical instruments. Several decontamination methods have been studied using the 263K-hamster prion; however, no studies have directly evaluated human prions. A newly developed in vitro amplification system, designated real-time quaking-induced conversion (RT-QuIC), has allowed the activity of abnormal prion proteins to be assessed within a few days. RT-QuIC using human recombinant prion protein (PrP) showed high sensitivity for prions as the detection limit of our assay was estimated as 0.12 fg of active prions. We applied this method to detect human prion activity on stainless steel wire. When we put wires contaminated with human Creutzfeldt–Jakob disease brain tissue directly into the test tube, typical PrP-amyloid formation was observed within 48 hours, and we could detect the activity of prions at 50% seeding dose on the wire from 10^2.8 to 10^5.8 SD₅₀. Using this method, we also confirmed that the seeding activities on the wire were removed following treatment with NaOH. As seeding activity closely correlated with the infectivity of prions using the bioassay, this wire-QuIC assay will be useful for the direct evaluation of decontamination methods for human prions.

Transmission of infection by flexible gastrointestinal endoscopy and bronchoscopy

Flexible endoscopy is a widely used diagnostic and therapeutic procedure. Contaminated endoscopes are the medical devices frequently associated with outbreaks of health care-associated infections. Accurate reprocessing of flexible endoscopes involves cleaning and high-level disinfection followed by rinsing and drying before storage. Most contemporary flexible endoscopes cannot be heat sterilized and are designed with multiple channels, which are difficult to clean and disinfect. The ability of bacteria to form biofilms on the inner channel surfaces can contribute to failure of the decontamination process. Implementation of microbiological surveillance of endoscope reprocessing is appropriate to detect early colonization and biofilm formation in the endoscope and to prevent contamination and infection in patients after endoscopic procedures. This review presents an overview of the infections and cross-contaminations related to flexible gastrointestinal endoscopy and bronchoscopy and illustrates the impact of biofilm on endoscope reprocessing and postendoscopic infection.

Impact of a standardized protocol and antibiotic-impregnated catheters on ventriculostomy infection rates in cerebrovascular patients

BACKGROUND

Ventriculostomy infections create significant morbidity. To reduce infection rates, a standardized evidence-based catheter insertion protocol was implemented. A prospective observational study analyzed the effects of this protocol alone and with antibiotic-impregnated ventriculostomy catheters.

OBJECTIVE

To compare infection rates after implementing a standardized protocol for ventriculostomy catheter insertion with and without the use of antibiotic-impregnated catheters.

METHODS

Between 2003 and 2008, 1961 ventriculostomies and infections were documented. A ventriculostomy infection was defined as 2 positive CSF cultures from ventriculostomy catheters with a concurrent increase in cerebrospinal fluid white blood cell count. A baseline (preprotocol) infection rate was established (period 1). Infection rates were monitored after adoption of the standardized protocol (period 2), institution of antibiotic-impregnated catheter A (period 3), discontinuation of antibiotic-impregnated catheter A (period 4), and institution of antibiotic-impregnated catheter B (period 5).

RESULTS

The baseline infection rate (period 1) was 6.7% (22/327 devices). Standardized protocol (period 2) implementation did not change the infection rate (8.2%; 23/281 devices). Introduction of catheter A (period 3) reduced infections to 1.0% (2/195 devices, P=.0005). Because of technical difficulties, this catheter was discontinued (period 4), resulting in an increase in infection rate (7.6%; 12/157 devices). Catheter B (period 5) significantly decreased infections to 0.9% (9 of 1001 devices, P=.0001). The Staphylococcus infection rate for periods 1, 2, and 4 was 6.1% (47/765) compared with 0.2% (1/577) during use of antibiotic-impregnated catheters (periods 3 and 5).

CONCLUSION

The use of antibiotic-impregnated catheters resulted in a significant reduction of ventriculostomy infections and is recommended in the adult neurosurgical population.

Inactivation of prions by acidic sodium dodecyl sulfate

Prompted by the discovery that prions become protease-sensitive after exposure to branched polyamine dendrimers in acetic acid (AcOH) (S. Supattapone, H. Wille, L. Uyechi, J. Safar, P. Tremblay, F. C. Szoka, F. E. Cohen, S. B. Prusiner, and M. R. Scott, J. Virol. 75:3453-3461, 2001), we investigated the inactivation of prions by sodium dodecyl sulfate (SDS) in weak acid. As judged by sensitivity to proteolytic digestion, the disease-causing prion protein (PrPSc) was denatured at room temperature by SDS at pH values of < or =4.5 or > or =10. Exposure of Sc237 prions in Syrian hamster brain homogenates to 1% SDS and 0.5% AcOH at room temperature resulted in a reduction of prion titer by a factor of ca. 10(7); however, all of the bioassay hamsters eventually developed prion disease. When various concentrations of SDS and AcOH were tested, the duration and temperature of exposure acted synergistically to inactivate both hamster Sc237 prions and human sporadic Creutzfeldt-Jakob disease (sCJD) prions. The inactivation of prions in brain homogenates and those bound to stainless steel wires was evaluated by using bioassays in transgenic mice. sCJD prions were more than 100,000 times more resistant to inactivation than Sc237 prions, demonstrating that inactivation procedures validated on rodent prions cannot be extrapolated to inactivation of human prions. Some procedures that significantly reduced prion titers in brain homogenates had a limited effect on prions bound to the surface of stainless steel wires. Using acidic SDS combined with autoclaving for 15 min, human sCJD prions bound to stainless steel wires were eliminated. Our findings form the basis for a noncorrosive system that is suitable for inactivating prions on surgical instruments, as well as on other medical and dental equipment.

Reducing the risk of cross-contamination from transmissible spongiform encephalopathies

IN RESPONSE TO RECENT REPORTS from several major US medical centers regarding possible exposure of surgical patients to transmissible spongiform encephalopathies (TSEs), one institution developed guidelines to care for surgical patients with the preoperative diagnosis of "rule out TSE." BASED ON CURRENT sterilization technology, using disposable surgical instruments may be the safest way to eliminate concerns of iatrogenic transmission of TSE and reduce the number of hospital staff members who could be exposed to the TSE contagion. PERIOPERATIVE PRECAUTIONS that can be taken when patients are undergoing brain biopsy procedures to rule out TSE are detailed.

Disposable devices for measuring intraocular pressure: a clinical study to assess their accuracy

AIMS

We conducted a study to compare the accuracy of two commercially available disposable tonometry devices (the acrylic biprism, Tonosafe and the silicone shield, Tonoshield) with the standard Goldmann applanation tonometer (GAT).

METHODS

A total of 80 eyes of 40 patients were randomly assigned to two groups. Group A (40 eyes) had the intraocular pressure IOP measured using GAT and the acrylic biprism (Tonosafe), while Group B (40 eyes) had IOP measured using GAT and the disposable silicone shield (Tonoshield). IOP was measured using the GAT both before and after the disposable device and average of the two standard Goldmann readings was compared with the IOP measured using the disposable devices.

RESULTS

The mean difference in IOP in Group A was 0.29 mmHg (SD 0.54) (P=0.0018) while in Group B the mean difference in IOP was 2.09 mmHg (SD 1.23) (P<0.0001). The Altman-Bland method was used to assess the agreement between two methods of clinical measurement. This shows a positive bias of 0.29 (95% confidence interval (CI) 0.11-0.46) when using the disposable acrylic biprism and a positive bias of 2.09 (95% CI 1.69-2.48) with the silicone shield.

CONCLUSION

The IOP recorded using the disposable acrylic biprism (Tonosafe) was in close agreement with the standard GAT. However, IOP readings obtained with the silicone shield (Tonoshield) tend to be higher than with the standard GAT. These facts should be kept in mind when recording IOP in clinical situations.

Creutzfeldt-Jakob disease--identifying prions and carriers

Two major obstacles to be overcome in minimizing the possibility of transmitting Creutzfeldt-Jakob disease or variant Creutzfeldt-Jakob disease are associated with identifying the prion on disinfected surgical instruments and identifying carriers of the protease-resistant form of the prion. New developments indicate that the means for doing both soon may be available.

Creutzfeldt-Jakob disease: recommendations for disinfection and sterilization

Prion diseases constitute a unique infection control problem because prions exhibit unusual resistance to conventional chemical and physical decontamination methods. Recommendations to prevent cross-transmission of infection from medical devices contaminated by Creutzfeldt-Jakob disease (CJD) have been based primarily on prion inactivation studies. The recommendations in this article consider inactivation data but also use epidemiological studies of prion transmission, infectivity of human tissues, and efficacy of removing microbes by cleaning. On the basis of the scientific data, only critical (e.g., surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e., brain, spinal cord, and eye tissue) from high-risk patients--those with known or suspected infection with CJD--require special treatment.

Prion disease and medical devices

Prions are novel proteinaceous-infectious agents that have been implicated in transmissible spongiform encephalopathies. It is now generally accepted that noninfectious prion proteins are normally produced by the host and may undergo a conformational change to an abnormal, pathologic form, which appears to be responsible for disease symptoms. Many methods of decontamination and sterilization are claimed to be ineffective against prion proteins. Incidences of iatrogenic transmission of prions due to medical devices have been reported, and the recommended clinical practices when handling suspected cases are reviewed. Recent results with a peracetic acid based sterilant indicate that it may be a safe and effective means of prion inactivation on medical devices.