Infection Control Hotline
Sterilizer monitoring with biological indicators (BIs) is considered the gold standard since BIs actually test a sterilizer’s ability to kill specific strains of highly resistant organisms. Commercially available BIs consist of spores in or on a carrier, accompanied by culture medium with a color change pH indictor dye. Here, SPSmedical Supply Corp. educators address questions about these important quality assurance devices.
| Source Notes | |
CHUCK HUGHES is the general manager and lead educator for SPSmedical Supply Corp., Rush, N.Y. Certified as a health education teacher, he serves on numerous AAMI sterilization committees and has worked for more than 25 years in the manufacturing industry in R&D, regulatory affairs, microbiology, marketing and sterilization training. In 2004, he was awarded “Educator of the Year” by the ASHSCP Inland Empire Chapter of California and received the “Award of Honor” in 2005 from IAHCSMM. |
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| GARY SOCOLA is the vice president of scientific affairs for SPSmedical Supply Corp. He serves on numerous AAMI sterilization committees and supervises SPSmedical’s validation and testing services to medical device manufacturers. He has worked for more than 22 years in health care settings in the areas of biomedical engineering, sterilization, R&D, quality assurance, regulatory affairs and validation testing. | |
| MARIANN HUGHES is the director of marketing and sales for SPSmedical Supply Corp. She has a master’s degree in business and served on the 2007 ASHCSP educational committee. She travels the country speaking on sterilization topics, providing sales support to field representatives and performing courtesy audits to hospitals and ambulatory surgery centers for compliance with sterilization standards. | |
Q: What standards are available for BIs?
Chuck Hughes: Numerous ISO (International Organization for Standardization) documents are directed toward manufacturers that AAMI (Association for the Advancement of Medical Instrumentation) has adopted as U.S. standards. For example, ANSI/AAMI/ISO 11138 Part 1 specifies general requirements for production, labeling, test methods and performance requirements for manufacturing BIs; Parts 2-5 cover specific requirements depending on the sterilization process. ANSI/AAMI/ISO 14161 provides guidance regarding the selection, use and interpretation of results of BIs when used to develop, validate and monitor sterilization processes; whereas ANSI/AAMI/ISO 18472 covers requirements for equipment called “resistometers” used to test the performance of BIs. Resistometers differ from conventional sterilizers as they require precise control, rapid rates of change and stringent accuracy measurement. It is because of these differences that BIs (and CIs) validated in a resistometer will perform much differently in commercial sterilizers used in health care facilities. The following user standards cover the selection and use of BIs: ANSI/AAMI ST79 Comprehensive Guide to Steam Sterilization and Sterility Assurance in Healthcare Facilities (see Section 10 Quality Control), ANSI/AAMI ST41 Ethylene Oxide Sterilization in Healthcare Facilities (see Section 7 Quality Control), and ANSI/AAMI ST58 Chemical Sterilization and High Level Disinfection in Healthcare Facilities (see Section 9 Quality Control).
Q: Can the same BI be used for all sterilizer processes?
Gary Socola: No. The organisms used for traditional sterilization processes are well documented. However, for any nontraditional sterilization processes, it is the responsibility of the sterilizer manufacturer to document the most resistant organism to their process. This information then becomes part of the manufacturer’s FDA clearance. Steam, hydrogen peroxide, ozone, chemical vapor and peracetic acid sterilization processes are monitored with Geobacillus stearothermophilus spores, while ethylene oxide (EO) gas and dry heat sterilization processes are monitored with Bacillus atropheus spores.
For consistency in testing, AAMI standards recommend health care workers place the BI in a process challenge device (PCD) to properly challenge the sterilization cycle.
PCDs can be made in-house following AAMI guidelines or purchased premade from suppliers. Depending on the type of sterilizer being tested and the type of monitoring (routine versus installation), PCD assembly and placement will vary. After processing, the BI is removed, activated and then typically incubated at 55 degrees to 60 degrees Celsius for Geobacillus stearothermophilus or 35 degrees to 37 degrees Celsius for Bacillus atropheus spores. Incubation time for conventional spore growth ranges from 16 hours to seven days, depending on the manufacturer’s validated incubation time cleared through the FDA.
Q: How often should sterilizers be monitored with a BI?
Mariann Hughes: According to AAMI standards, health care facilities should use BIs to monitor steam sterilizers at least weekly, preferably daily and for every load that contains an implant. EO gas sterilizers should be monitored every load, while hydrogen peroxide, ozone and peracetic acid sterilizers should be monitored at least daily, preferably every load. Furthermore, each day a sterilizer is monitored, one unprocessed BI (from the same lot) should be incubated as a control to verify the pre-sterilization viability of the spores, the ability of the media to promote growth and proper incubation temperature.
If the control BI fails to grow, it should be assumed that the BIs from that lot are nonviable or improper incubation has occurred. Routine BI testing should always be performed with a load, except for flash sterilizers, which should be tested in an open tray and inside a rigid container (if used) without a load. For loads containing implants, a Class 5 integrator should accompany the BI inside the PCD. Non-implant items may be released immediately based on the Class 5 integrator results; however, implants should be quarantined until results of the BI testing are known. In emergency situations, implants may be released on the Class 5 integrator results with documentation fully traceable to the patient.
Q. What are some common causes of sterilizer failure?
C. Hughes: Overloading, improper loading, running from a cold start, incorrect cycle selection, incomplete air removal and/or poor steam quality are common causes of sterilizer failure. While sterilizers can and do mechanically fail, it is estimated that 85 percent of sterilizer failures are caused by operator error. Staff education is critical to avoid positive BI (nonsterile) results, which can lead to product recalls. Of additional concern are false negative (sterile) results, where the BI shows no growth during incubation when the sterilizer cycle has failed. This can occur by using an incorrect BI, an incorrect PCD, an improperly placed PCD, failure to activate the BI, an unplugged incubator, improper incubator maintenance and/or auto-reader calibration. To avoid unnecessary recalls or the release of suspect loads, health care personnel must be well trained in the four types of BI results, which are positive, negative, false positive and false negative.
Q: What should be done if the sterilizer fails a BI test?
Socola: According to AAMI standards, the following actions should be taken in the case of a positive BI test:
1. Report results to supervisor. Record time and date of questionable sterilizer cycle, description of load and lot number, results of gauges and chemical indicators, along with any other information that could be useful in determining whether the results are mechanical versus operator error.
2. If the failure was mechanical, items should be recalled back to the last negative BI.
3. The microbiology lab should perform a presumptive identification to verify spore growth. The load recall should not be delayed during this testing.
4. Department heads, facility maintenance and sterilizer service personnel should determine cause of failure and arrange for corrective action.
5. Rechallenge the sterilizer with a PCD in three consecutive empty chamber cycles before using again. For dynamic-air-removal sterilizers, a Bowie-Dick test pack also should be run in three consecutive empty-chamber cycles. Until the results of retesting are satisfactory, the sterilizer should be taken out of service.
Q: What role does the microbiology lab play with positive BI test results?
M. Hughes: For positive BIs, the microbiology lab should confirm that the growth is indeed the test organism and not a contaminate that occurred during activation or transfer. Per AAMI standards, two subcultures are made from the recovered culture with one incubated at 35 degrees to 37 degrees Celsius for 24 to 48 hours and the other at 55 degrees to 60 degrees Celsius for 24 to 48 hours. Smears of the incubated subcultures are prepared, gram stained and microscopically examined. Any result that is not gram-positive cocci or gram-negative bacilli is considered a contaminant. This would confirm operator error and there is no need to recall back to the last negative BI.
Q: Are there any special concerns with BI monitoring of extended cycles?
C. Hughes: Yes. ANSI/AAMI/ISO 14161 states: “Users should not over process the culture medium, as extended sterilization can induce changes that can affect its growth promotion properties. The ability of the culturing medium to promote the growth of a low number of microorganisms should be demonstrated.”
About this column
This column presents answers and practical guidance to some of the most commonly asked questions of suppliers and educators in the infection control and sterile processing communities. To submit a question to the column, e-mail Bob Kehoe, executive editor, at [email protected].
This article first appeared in the February 2009 issue of Materials Management in Health Care.
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