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Biological indicators

Clinical relevance

SSI markets quality-assured biological indicators (BI) - also known as spore tests - to test sterilisation processes.
Every sterilisation process must be tested to ensure compliance with the values for critical physical parameters such as temperature, time, pressure, humidity and gas concentration. The cause of any deviations in the specified parameters must be identified immediately, and the error rectified.
Biological indicators are used for microbiological testing to ensure that microorganisms present are indeed killed by a particular sterilisation process. BIs are recommended for periodic testing and validation of sterilisation equipment.

Background

Biological indicators are preparations of selected microorganisms with high resistance to specific sterilisation methods, e.g. steam or dry heat sterilisation. BIs are calibrated against a well-defined resistance, so that inactivation of the microorganisms in the spore sample shows that the sterilisation process has been effective.

BIs are used to validate and test sterilisation processes. All new sterilisers and new procedures, e.g. those resulting from changes in the sterilisation programme or in the packaging of goods, should be validated. The sterilisation processes should then be tested regularly with BIs distributed in the items to be sterilised - preferably positioned in places where it is difficult for heat and steam to penetrate. In the case of non-validated equipment, more frequent testing with BIs should be carried out, as the lack of validation means the sterilisation process is less reliable. After exposure, BIs are sent in the accompanying franked return envelope for analysis by SSI. Analyses can also be carried out in an in-house laboratory.
It is recommended that 6 BI units be used (3 units for small sterilisers) in every cycle when carrying out routine testing.
The use of indicators is suitable for anyone needing to test sterilisation processes, e.g. hospitals, the pharmaceuticals industry and the primary care sector.

Competence

Statens Serum Institut is the sole supplier of biological indicators from the firm Simicon to test steam, dry heat and formaldehyde sterilisation. Culturing of the biological indicators can also be ordered from Statens Serum Institut, which immediately informs the customer if any growth is found in one or more units. In addition, a subscription scheme is offered to small clinics requiring regular testing.

Quality

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