SN 2002(11) - Benchtop vacuum steam sterilizers - the "prion cycle"

Please note that contact names and/or numbers may have changed since this notice was published. If you need to contact us about a particular notice, email dts@mhra.gsi.gov.uk quoting the reference number and title of the notice.
_________________________________

March 2002

MANUFACTURER/SUPPLIER
Generic

PROBLEM
Users and potential purchasers of benchtop vacuum steam sterilizers should not be misled that a so-called 'prion cycle' alone will minimise the risk of prion transmission.

For the attention of:

NHS Trusts (England) - Chief Executives
National Care Standards Commission - Headquarters
Primary Care Trusts (England) - Chief Executives

ACTION

1. Whenever practicable

• Use single use devices
• Use a Sterile Services Department to reprocess reusable devices.

2. Clean all instruments thoroughly, preferably using a mechanical method before sterilization.

3. Consult your infection control team if you consider that a patient has, or is in an 'at risk' category of having, Creutzfeldt-Jakob Disease (CJD).

4. Follow the Advisory Committee on Dangerous Pathogens (ACDP) Spongiform Encephalopathy Advisory Committee (SEAC) guidance on risk assessment of patients with, or at risk of having, CJD.

DISTRIBUTION REQUIRED
Please bring this notice to the attention of all who need to know or be aware of it . This will include distribution by:

TRUSTS to:

• Liaison Officers (for onward distribution)
• Medical directors
• Nurse executive directors
• Outpatients departments
• A&E departments

PRIMARY CARE TRUSTS to:

• Liaison Officers (for onward distribution)
• General Medical Practitioners
• General Dental Practioners
• Practice Nurses
• Chiropodists

NATIONAL CARE STANDARDS COMMISSION to:

• Headquarters (for onward distribution)
• Nursing Homes
• Hospices
• Hospitals in the Independent Sector
• Residential Care Homes

BACKGROUND
Many benchtop steam sterilizers being placed on the market now feature a so-called 'prion cycle', which is a cycle of 18 minutes hold time at 134-137°C. Exaggerated claims have been made for the effectiveness of that cycle for the inactivation of prions. Users and prospective purchasers should be aware that this cycle alone will not inactivate prions completely.

An abnormal form of prion protein (prion) is generally considered to be the probable means of transmission of CJD, which is one of a group of fatal degenerative brain diseases known collectively as Transmissible Spongiform Encephalopathies (TSEs).

Thorough cleaning is considered to give a substantial reduction in the level of contamination on devices and to minimise the theoretical risk of cross infection with CJD. This is a very rare disease and the risk of transmission through reuse of reusable medical devices is unknown.

The ACDP and the SEAC have jointly published guidance* on control of infection by these agents in clinical settings. It includes a sterilization cycle of 18 minutes hold time at 134-137°C (or 6 consecutive cycles of 3 minutes each at 134-137°C) in a properly functioning porous load steam sterilizer. This cycle alone will not inactivate prions completely.

TSE agents are unusually resistant to conventional chemical and physical decontamination methods and the recommended autoclaving cycles may not be entirely effective in inactivating prion protein. The Department of Health has issued guidance on the importance of cleaning to minimise the risk of cross infection with TSEs via reusable medical devices (HSC1999/178 - variant Creutzfeld-Jakob Disease (vCJD) : Minimising the Risk of Transmission).

The ACDP/SEAC guidance* on infection control in clinical settings contains a risk assessment to help medical practitioners to identify patients at risk of suffering with a TSE and also classifies the risk categories of various tissues that contain abnormal prion protein. Guidance is provided on appropiate measures to minimise the risk of cross infection via medical devices that have been used on those patients. The guidance is intended for both hospital and community care. You should refer to this guidance if you are treating a patient known, or suspected, to be suffering from neurodegenerative disorders.

*Transmissable spongiform encephalopathy agents: safe working and the prevention of infection. Advisory Committee on Dangerous Pathogens Spongiform Encephalopathy Advisory Committee - The Stationery Office, London, 1998

ENQUIRIES
Enquiries to the MHRA should quote reference number 20020218.018-12

© Crown Copyright 2002