INFECTION PREVENTION & CONTROL
Biological indicators used for these applications are usually cited to conform to the EN ISO 11138 series;5
specific parts
of this series give particular requirements for BIs for the various sterilisation methods, however there are no BI standards for radiation sterilisation (this process is used industrially and is controlled using dosimeters and not BIs) and currently no standards for vapour-phase hydrogen peroxide BIs, although there is work in progress to publish a standard in this area. Regulatory bodies may require that manufacturers of sterile products use specific monitoring methods to ensure sterility; for example, the US Food and Drug Administration (FDA) will require use of BIs as part of the sterilisation process monitoring. In Europe, the User is a defined term for the person responsible for the sterilisation process; the User is often, for example, the sterilisation department manager, and they will have responsibility to determine the most appropriate methods to monitor the sterilisation process, typically using the ISO standards mentioned above. Regardless of the sterilisation process or the geographic area, it is of course necessary to justify why a particular sterilisation monitoring method is used. There is no such thing as a perfect monitor, so the inadequacy of one method can be supported by other methods. For example, in steam sterilisation, the variables necessary for microorganism destruction are time, presence of moisture and temperature. Time is readily measured, and, while temperature can be measured accurately in the chamber drain, this is not necessarily correlated to the temperature within the load to be sterilised. Hence chemical indicators are used within the load to support the temperature probe readings;
incubation temperature and recovery media meant that this incubation time could be shortened to 24 hours or less. Using advanced methods for the detection of microorganism germination such as fluorescence, this incubation time can be shortened to as little as 20 minutes.
Conclusion
The Browne TST Control Emulating Type 6 Indicators provide ‘in pack’ verification of steam sterilisation cycles
there are no direct methods for determining presence of moisture (typically steam), hence chemical indicators are used daily as part of the Bowie Dick test to assess steam penetration. BIs or CIs may also be used within the load or within process challenge devices to verify presence of steam and adequate removal of air. Sterilisation processes such as vapour- phase hydrogen peroxide may use a combination of physical measurements, BIs and CIs to verify attainment of the required process variables. Another factor to consider when using BIs is the time available to release the load; in industrial applications, the time taken to release a load may not be as critical as within a hospital, when reusable medical devices need to be released for use on patients. In these cases, use of a BI industrially may have no significant time consequences, but clearly would do within a hospital setting; the time taken to get confirmation of the biological indicator result is continually getting shorter with advances in technology.
Historically the BI incubation time was seven days; definition of such factors as
There are many factors - scientific, pragmatic, regulatory or regional - that will dictate what monitoring is required of specific sterilisation processes. As technological advances in biological, chemical and parametric monitoring occur, the more flexibility will exist in the options that are available for sterilisation monitoring.
References
1 ISO 14937 Sterilisation of health care products — General requirements for characterization of a sterilizing agent and the development, validation and routine control of a sterilisation process for medical devices
https://www.iso.org/standard/ 44954.html
2 ISO 17665 Sterilisation of health care products — Moist heat — Part 1: Requirements for the development, validation and routine control of a sterilisation process for medical devices
https://www.iso.org/standard/43187.html
3 ISO 11135 Sterilisation of health-care products — Ethylene oxide — Requirements for the development, validation and routine control of a sterilisation process for medical devices
https://www.iso.org/standard/56137.html
4 ISO 11137 Sterilisation of health care products — Radiation — Part 2: Establishing the sterilisation dose
https://www.iso.org/standard/62442.html
5 EN ISO 11138 Sterilisation of health care products — Biological indicators — Part 5: Biological indicators for low-temperature steam and formaldehyde sterilisation processes
https://www.iso.org/standard/66448.html
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