3.4.1.1 Production of Process Challenge Devices (PCD)
A Process Challenge Device (PCD) is a microbiological challenge system used to evaluate the kill rate of selected process parameters. It is typically a device or test package containing biological indicators (e.g., Bacillus atrophaeus spores with known spore count). The resistance of the PCD to the sterilization process should be greater than or equal to the resistance of the natural microbial load in the most difficult-to-sterilize area of the product. The quantity of PCDs should meet the requirements outlined in Table C.3 of Appendix C in GB18279.1-2015. PCDs are classified into Internal PCDs (IPCD) and External PCDs (EPCD).
a)Internal PCD (IPCD) Production
Internal PCDs are typically medical devices selected by the company to represent a product family. Based on design and material composition, these products are considered some of the most difficult to sterilize. Biological indicators (BI) are placed at the most difficult-to-sterilize position of the product, ensuring that the sterilization process does not block the channels or interfere with the product design.
Place the biological indicator (BI) in the most difficult-to-sterilize area of the product, or inoculate the test microorganism (e.g., Bacillus atrophaeus) in the location with the most difficult-to-achieve sterilization conditions.If the BI or test microorganism cannot be placed at the hardest-to-sterilize location, an alternative device can be designed and placed within a sterile barrier system, ensuring that it has the same resistance as the hardest-to-sterilize location in the product.
Common IPCDs include, but are not limited to:
Placing the contaminated carrier between components such as rings, piston heads, washers, or syringe pistons.Placing the microorganism challenge in the middle of a catheter lumen, then using adhesive solvents or connectors to reseal the catheter and restore the product’s integrity.Placing the microorganism challenge at the piston interface.
b)External PCD (EPCD) Production
External PCDs are placed on the outside of the loaded product. EPCDs are typically used for routine processing and are retrieved from the load after treatment. The resistance of the EPCD to the biological load of the sterilized product should be compared with the IPCD’s resistance. The EPCD should also represent the most difficult-to-sterilize product in the load.
The relationship between EPCDs and contaminated product samples should be periodically reviewed to ensure that no changes have occurred in the sterilized product and that the EPCD still represents the most difficult-to-sterilize product in the load.
When placing a BI in a PCD, the PCD should have at least the same resistance as the most difficult-to-sterilize location in the product.
Common EPCDs include, but are not limited to:
Placing a biological indicator (BI) inside product packaging or equivalent, such as plastic bags, which is then placed inside a Manila envelope.Placing a biological indicator in a thick plastic bag that has been folded a specified number of times.Placing the biological indicator in various parts of a syringe, such as in the piston washer or piston head.Sealed plastic tubes containing contaminated carriers, with or without additional packaging.
PCDs produced in the above manner are packaged using the same methods as regular production products, evenly distributed within the product load, and positioned to cover the cold spots within the sterilizer chamber.
3.4.1.2 Partial Cycle (Short Cycle) Testing
After selecting the PCD, its suitability is confirmed by running a partial cycle. The evaluation method is as follows:
a) Determine the placement methods for PCDs, test samples, and sensors based on the results of the operational evaluation. The number and distribution of PCDs should be sufficient. If the selected EPCD is used for routine sterilization process monitoring, it should be placed on the product load according to the plan and procedure.
b) Based on the D value, ST time, and KT time of the biological indicator, set a shorter exposure time. Other parameters should be tested at the lower limit of routine sterilization process parameters. The test method should refer to Appendix A of GB18281.2. After the exposure time ends, remove the product, IPCD, and EPCD for microbial cultivation and observe the results.
The cultivation results should show that the resistance of the PCD is greater than or equal to the biological load resistance of the hardest-to-sterilize location in the product:
IPCD and EPCD should be partially negative; a fully negative or fully positive result would indicate test failure.The resistance of the IPCD should be greater than the product, and the resistance of the EPCD should be greater than or equal to that of the IPCD.
If the results do not meet expectations, investigate the cause. Typically, adjustments to the PCD resistance or sterilization parameters are needed, followed by retesting until the results align with expectations. If all three (product, IPCD, and EPCD) show no microbial growth, reduce the EO exposure time appropriately and test again. If all show microbial growth, increase the EO exposure time and retest.
3.4.1.3 Half-Cycle Testing
After successfully completing short-cycle testing, run three consecutive consistent half-cycle tests to demonstrate the effectiveness (SAL = 10^-6) and reproducibility of the EO sterilization process. The evaluation method is as follows:
Set the biological indicator’s sterility as the standard, and set other sterilization process parameters to the lower limit of routine sterilization parameters (e.g., pre-treatment transfer time within the specified range). Gradually halve the sterilization exposure time of the initial sterilization process and remove biological indicators from the PCD after different sterilization times. Cultivate them in a sterile environment until sterility is confirmed. The shortest sterilization time (critical time) thus determined will be the half-cycle time, and at least two more tests should be conducted with the same shortest time.
All three test results should show complete inactivation of all biological indicators (initial colony count no less than 1×10^6) to confirm the minimum effective EO exposure time. The exposure time in the routine sterilization process should be at least twice this minimum time.
The biological indicator cultivation results should show all IPCDs and EPCDs negative. If the short-cycle test shows that the EPCD’s resistance is greater than that of the IPCD, the EPCD may show partial positivity.
If the results do not meet expectations, investigate the cause and usually adjust the sterilization parameters before retesting until the results align with expectations.
Example:
Assume the first half-cycle sterilization exposure time is 4 hours. If sterile, reduce the exposure time to 2 hours for the next test; if microbial growth occurs, increase the exposure time based on the 4-hour exposure.
Assume the second half-cycle sterilization exposure time is 2 hours. If sterile, reduce the exposure time to 1 hour for the next test; if microbial growth occurs, extend the exposure time to 3 hours.
Assume the third half-cycle sterilization exposure time is 3 hours. If sterile, repeat the 3-hour test twice. If all results are sterile, confirm 3 hours as the minimum effective time. If microbial growth occurs, repeat the test with 4-hour exposure, and if all results are sterile, confirm 4 hours as the minimum effective time.
3.4.1.4 Full Cycle Testing
During full cycle testing, set the EO exposure time to twice the half-cycle minimum effective time, and other parameters to the upper limit of routine sterilization parameters to verify the reliability and reproducibility of the sterilization process.
The number of temperature and humidity sensors used should meet the requirements of Appendix C in GB18279.1, evenly distributed within the sterilization load. Temperature sensor placement points should include both the cold and hot spots within the sterilizer chamber during the Operational Qualification (OQ).
After the test, the cultivation results of the product and EPCD should show complete sterility (all negative).
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| ISO 14161:2009 | Sterilization of health care products — Biological indicators — Guidance for the selection, use and interpretation of results |
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| ISO 11737-2:2009 | Sterilization of medical devices — Microbiological methods — Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilization process |
| AAMI TIR16:2017 | Microbiological aspects of ethylene oxide sterilization |