Quality control of sterilization processes You can’t see sterility. This basic fact drives the need for a quality control system that provides information on the quality of a sterilization process, so a decision can be made on whether or not the processed instruments are safe for patient use. The American National Standards for the key healthcare sterilization processes: steam, ethylene oxide, and vaporized hydro- gen peroxide, all recommend the integrated use of three quality control monitoring tools: physical monitors, chemical indicators, and biological indicators.4,5,6

The information

provided by each tool is different. Physical monitors are electronic sensors inside the chamber that provide data on the environ- ment inside the sterilizer chamber such as the temperature or pressure. This data is recorded on a printout that can also be used as a record of the cycle. Review of cycle printouts from the physical monitors can confirm that the proper cycle was selected. The second quality control tool, chemical indicators, utilize specially selected chemicals that respond to the effects of the sterilization process. Chemical indica- tors that are used on the outside of packages (Type 1 process indicators) can provide visual evidence that an item has gone through the sterilizer. Common process indicators include indicator tapes and chemical dots printed on packages. Remember that process indicators are only designed to indicate exposure to the sterilant, and they do not provide evidence that the process was effective. The more sophisti- cated chemical indicators (Type 5 and Type 6 indicators) that are used inside of containers and packages are designed to respond to all the sterilization process variables. These chemical indicators provide more detailed information on whether the required process conditions were achieved on the inside of the packages.

As we have discussed, the third quality control tool, biological indicators, are used to directly measure the effectiveness of the sterilization process by measuring its effect on live microorganisms. Let’s take a closer look at the role of biological indicators in the quality control of sterilization processes.

The role of biological indicators in quality control

Biological indicators are placed with the load inside of the sterilizer chamber in the location determined to be the most difficult to sterilize. The typical biological indicator placement location for large steam sterilizers is over the drain; for ethylene oxide sterilizers, in the center of the load, and for hydrogen perox- ide sterilizers at different chamber locations

Sponsored by

specific to the sterilizer, cycle, and load. The instructions of the sterilizer manufacturer re- garding the recommended placement location for the biological indicator in their sterilizer should be followed.

Biological indicators are typically used inside of process challenge devices (PCDs) or other items that can represent the steril- izer load. Placement of biological indicators inside of the containers or packages would give direct information on the lethality of the sterilization process inside the device packag- ing, but this placement is not practical as even today’s rapid readout biological indicators require incubation time that would not be feasible in the OR. So, biological indicators are placed into PCDs or other devices that are intended to have the biological indicator perform as if it was placed inside of containers or packages in the load. Reference PCDs that can be constructed in healthcare facilities are described in the standards.4,5


available PCDs that have been cleared by the Food and Drug Administration (FDA) with performance equivalent to the reference PCDs are also available. These devices eliminate the need for staff time to assemble test packs, and are typically more consistent because of automated assembly processes and quality control procedures required of medical device manufacturers.

The recommended frequency of use of biological indicators in healthcare facilities varies by the sterilization process. For steam, the recommendation from AAMI is weekly use, but preferably daily use, for routine ef- ficacy monitoring. Also, a biological indicator should be used to release any load containing an implantable device. Implant-loads should be quarantined until the biological indicator results are available.4

Per AAMI, a biological

indicator should be used to monitor every load for ethylene oxide sterilization processes. Again, any implants should be quarantined until the biological indicator results are avail- able.5

for every sterilization load, regardless of the device, intended use, day of the week, etc.7,8,9

It is curious that reusable medical

devices reprocessed in a healthcare facility do not have to meet the same level of safety as those sterile devices received directly from manufacturers. Many healthcare facilities are now leveraging the significant reductions in biological indicator incubation time to increase their frequency of use of this important QC tool, without negatively affecting their work flow. For example, rapid readout BIs make the quarantine of implantable devices until the biological indicator test result is available much more realistic. Many hospitals have moved to monitoring of every sterilization load with biological indicators even where the current healthcare standards do not require it, such as for steam and vaporized hydrogen peroxide. Load items from these processes are not distributed until a negative BI result is obtained. The criteria often cited for mak- ing this change include a desire to improve quality control to assure a uniform standard of care for all patients, avoidance of the extra work required in the event of a recall, as well as reduction of errors in the sterile processing department caused by varying requirements for biological indicator monitoring.

Finally, for vaporized hydrogen perox- ide processes, the AAMI recommendation is that biological indicators be used daily, but preferably in every load. The same require- ment of BI monitoring with load quarantine until the BI results are available is applied for implants.6

As you can see, there is some variability in the current recommended practices regarding frequency of use of biological indicators. It is interesting to note that this type of variation is not allowed for medical device manufacturers that are supplying sterile, single-use devices to healthcare facilities. National and international standards for medical device manufactur- ers require the same level of quality control


Summary Biological indicator technology has continued to evolve with faster detection of the biological signals produced by the bacterial spores that provide the direct challenge to the sterilization process. These technologies have resulted in biological indicators with incubation times of less than 30 minutes for some sterilization processes. These short incubation times now make it possible to obtain biological test results in time for optimized instrument workflow, including shorter quarantine periods for implantable devices, and in many facilities, for all instruments. These indicators can facili- tate improved quality control of sterilization processes by enabling increased frequency of biological monitoring. HPN


1. ISO/TS 11139: 2005. Sterilization of healthcare products — Vo- cabulary. International Organization for Standardization.

2. Guideline for Disinfection and Sterilization in Health Care Facilities. WA Rutala, DJ Weber (ed). Centers for Disease Control and Preven- tion. 2008.

3. ANSI/AAMI/ISO 11138-1:2017. Sterilization of healthcare prod- ucts — Biological indicators — Part 1: General requirements. Associa- tion for the Advancement of Medical Instrumentation, Arlington, VA.

4. ANSI/AAMI ST79:2017. Comprehensive guide to steam steriliza- tion and sterility assurance in healthcare facilities. Association for the Advancement of Medical Instrumentation, Arlington, VA.

5. ANSI/AAMI ST41:2008/(R)2012. Ethylene oxide sterilization in healthcare facilities: Safety and effectiveness. Association for the Advancement of Medical Instrumentation, Arlington, VA.

6. ANSI/AAMI ST58:2013. Chemical sterilization and high-level disinfection in healthcare facilities Association for the Advancement of Medical Instrumentation, Arlington, VA.

Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62