Indicators of sterility: Mechanical, chemical, biological
by Susan Cantrell, ELS

3M Attest -BI reading

Don’t be fooled into judging the importance of biological indicators (BIs) by their size. They may appear small and insignificant but they can reveal something big and extremely important to patient safety. BIs are akin to canaries in the coal mines or frogs in the ecosystem: they serve as monitors for the presence of unseen, potentially life-threatening, dangers. BIs monitor specifically for survival of pathogens during the sterilization process.

Monitoring sterilization
Monitoring the sterilization process is vital to infection control. Evaluation of the sterilizer, personnel, and materials used should be performed on an ongoing basis.

Heide Ames, Associate Product Manager, STERIS Corp, Mentor, OH, offered insight into the sterilization process: "The process is more than the act of sterilization. Process control starts with proper pretreatment of soiled items and ends with aseptic transfer of the sterile items to the point of use." Sandra Lee, Senior Manager, Professional Education, STERIS, continued, "Policies and procedures written according to the Association for Advancement of Medical Instrumentation (AAMI)-, Association of Operating Room Nurses-, and Association of Practitioners in Infection Control-recommended standards and practices are essential. Training staff and auditing staff performance all contribute to process control. Operating room, central supply, and infection control managers must work together to create a standardized and effective system for patient safety."

Mechanical, chemical, and biological indicators
BIs are one of three ways used to monitor the sterilization process:

STERIS Verify Dual Temp Incubator

Mechanical (or physical) monitoring is performed outside the sterilizer by observing things such as displays, gauges, and computer printouts that evaluate the sterilizer’s functions such as time, temperature, and pressure. Mechanical monitoring may be the first indicator to show that something has gone awry.

Chemical monitoring is used to evaluate the conditions inside the sterilizer. Color changes of the chemicals indicate whether the items placed inside the sterilizer have been exposed to sterilization agents and whether the proper conditions were present for sterilization to occur. If the expected change in chemicals does not occur, it may indicate equipment malfunction or procedural error.

Biological monitoring uses spores inoculated onto an object such as a strip that is placed inside the sterilizer. If the spores die, it’s an indicator of successful sterilization.

3M Attest Rapid Readout

"The bugs don’t lie," but . . .
Charles Hancock, Medical Device Sterilization Consultant, Charles O. Hancock Associates, Inc, Fairport, NY, told HPN: "For quality purposes, the BI, essentially a population of bacterial spores, is considered industry-wide to be the basic measure of the efficacy of the lethal sterilization process." Ames explained why: "BIs represent the best challenge to a sterilization process simply because they are living microorganisms. They contain bacterial spores that are magnitudes more resistant to sterilization than the typical pathogenic organisms. If those spores die, it provides assurance that pathogenic organisms did not survive the sterilization process." While it’s not an indication of device sterility, as Hancock pointed out, "It offers a sterility assurance level (SAL) of 10-6, a probability that one in a million spores survived the process." Chris R. Dwyer, Director International Sales, Raven Biological Laboratories, Omaha, NE, recalled a popular saying throughout the industry: "The bugs don’t lie."

3M Comply Steri Gage

Lee expounded: "A negative result doesn’t ensure that every item in the load has been sterilized; it simply indicates the sterilization cycle was delivering the appropriate parameters to kill the test microorganisms, nothing more."Gale Havrilla, 3M Technical Services Specialist, St. Paul, MN, explained further why a test may show negative when in fact it isn’t: "While BIs provide evidence that the set of sterilization conditions employed were able to destroy microbes and that the equipment is working properly, they may not detect localized problems within the chamber due to packaging or loading errors, because BIs generally are placed at a single location."

Dwyer, emphasized how important it is to load, and not overload, sterilizers, since it can interfere with the sterilization process: "Defining and practicing validated loading patterns is a major concern, because an overloaded tray can cause sterilization failure. It’s important to place the BI as close to the center of the pack or tray as possible; when not possible, a multiparameter CI should be placed there. Placing a BI next to or outside of an overloaded tray does not give an accurate representation as to what is happening inside the tray. Placing a BI or CI next to or outside of a densely loaded pack would be like placing a meat thermometer next to your thanksgiving turkey instead of inserting it into the meat. The thermometer will tell you how hot it is on the outside, but you want to make sure the inside has reached the right temperature before you eat it."

BI, CI, or both?
Whereas BIs are the most important check on the sterilizer function, it’s important to use them in conjunction with CIs. It would be a mistake to rely primarily on CIs, because dead bacteria are what really tell the tale. Havrilla referred to AAMI’s position on the matter: "AAMI clearly indicates that chemical integrators cannot replace BIs but should be used with them to provide additional information."

Raven ProChem B-D

Nevertheless, "using multiple CIs in every pack is desirable," said Havrilla, "to show whether the sterilant penetrated the pack and reached the item to be sterilized, but in practice it is not done frequently. In theory, if the most difficult location to achieve sterilization in a specific pack or container has been determined by testing, then a single CI in this location could be argued to be adequate."

Dwyer confirmed the importance of using BIs and CIs in tandem: "BIs and CIs are an integral part of a complete sterility assurance program. Both have value in protecting patients from infection when used according to the guidelines. Multiparameter CIs are inexpensive and are great for ensuring that sterilization is approximated in many places throughout the cycle; however, multiparameter doesn’t equal every parameter when the goal is biological kill. BIs best challenge the process to see if it can deliver a lethal cycle."

CIs can often but not always detect failures in the sterilization process, explained Havrilla. "Chemical integrators cannot detect common sterilization failures such as incomplete air removal and superheated steam conditions that can be generated within individual packs. Research published in Disinfection, Sterilization and Antisepsis: Principles, Practices, Challenges, and New Research, edited by William A. Rutala, published by APIC, has proven that these common sterilization failures can be detected only by BIs and cannot be detected by CIs, including chemical integrating indicators. Biological monitoring is the only method that can detect any set of conditions that fails to destroy microorganisms."

STERIS Verify Activator Set

"BIs and CIs have separate and distinct functions," stressed Lee. The difference in their functions was summed up by Hancock: "CIs show whether the minimum requirements for the sterilization process have been achieved, tracking parameters such as time, temperature, and humidity; BIs look at numerical counts of organisms. Along with mechanical monitoring, the three monitors should be used together to tell the whole story of the process. No one factor would really tell the complete story."

How often to use BIs?
"BIs should be used weekly, and preferably daily, to monitor each cycle type used in the sterilizer," said Lee. "In addition, BIs should be used within an appropriate challenge pack for every load containing an implant. Controls from the same lot must be performed each day that a BI is being used. The control should consist of an unprocessed BI incubated to confirm growth of the bacteria (positive control). In the case of the rapid-read BI, one BI a week should be additionally allowed to continue its incubation following the first read to confirm the bacterial kill (negative control)."

The advantage of frequent use, explained Havrilla, is that it "improves the ability to detect problems as soon as they arise and eliminates, or minimizes the extent of, a recall. In the event of a positive BI, it’s necessary to recall all loads since the last negative BI for that sterilizer. Cost of recalls should be factored in the determination of your monitoring frequency, since it’s necessary to recall all loads since the last negative BI. The greater the number of loads that need to be recalled, the greater the effort, cost, and risk posed to patients and the healthcare facility."

Hancock suggested users should think through why use of BIs is important: "The user should consider what he’d do if failure necessitated a recall. They should ask themselves, ‘How comfortable would I be if I went a week with using the equipment and then found out there had been a failure?’ The real bottom line in sterilization is risk to the patient. Users should look at the worst-case scenario: How comfortable would you feel explaining to survivors of the patient why something went wrong?"

New and improved BIs and CIs
According to Hancock, "The overall picture of the success of a sterilization cycle is much more accurate today than it was 10 years ago, because we have more and better information. In recent years, there has been significant improvement in the accuracy of CIs, and the enzyme readout has brought about dramatic improvement in BIs. Instead of growing organisms for 48 hours to determine success or failure, the answer is available in a couple of hours."

Havrilla agreed with Hancock’s assessment: "A key concern in the past has been the delay in availability of results. With standard BI technology, it has been necessary to wait a minimum of 24 to 48 hours for results. Healthcare professionals could either hold processed loads, pending the BI result, or gamble that the process was adequate, based on limited information, and release the load before BI results were available. New rapid-readout technology provides biological monitoring results within 1 to 4 hours, allowing goods to be released for use much sooner. Faster turnaround eliminates the need for duplicate sets of expensive instruments."

Ames explained how the enzyme-based readout works: "BIs with an enzyme-based read technology look for the activity of an enzyme found within a spore. Unlike the traditional indicator, this technology does not require bacteria replication; however, the enzyme can remain active even though the bacteria are dead, indicating a positive growth response. The next generation of BIs will combine the conventional BI’s ability to detect bacterial growth with the speed of an enzyme-based technology, while also eliminating the frequency of false positives."

Challenges and concerns
"The biggest challenge is for the user to understand what’s appropriate and how to assess his equipment," observed Hancock. Ames added, "BIs require incubators or readers that require maintenance, service, and calibration. These activities can be missed in the maintenance routine of the hospital staff. Malfunction or miscalibration of these devices can lead to false negatives and the possibility of a nonsterile item being used."

There might be the temptation to rely more on CIs than BIs, noted Havrilla. "Another concern with BIs is the cost when compared to relatively inexpensive and immediate visual results offered by chemical integrator technology. In developing monitoring policies, it’s important to consider the cost and time involved in a recall, the ability to defend any deviation from recommended practices or standards in the event of a lawsuit, and the implications of infections resulting from nonsterile instruments that were not detected by chemical integrating indicators."

"Many users don’t have a good understanding of the purpose of BIs or of the sterilization process," observed Hancock, "so, if something goes wrong, they may not have the tools to assess the seriousness of the situation. Some people don’t make the connection between their actions, or lack of action, and the patient’s outcome. Having more and better information available is not helpful to people who don’t understand how they can contribute to very serious infectious circumstances, particularly at the first level of disinfection, which is cleaning. If someone makes a mistake at the first level, it may not be correctable later."

Havrilla added, "With the high employee turnover in typical sterile processing departments, training and education of staff on the correct use of biological monitoring represents a challenge for managers." Hancock stressed the necessity of ongoing education for users: "It’s important to go back to the basics, pound it into people until they’re sick and tired of hearing it, until it finally affects their daily performance. Some of the worst offenders are those who should be the most knowledgeable. Some who know the most do least."

Lee concurred: "In the fight against nosocomial infections, it is important to remember that, often, it is the most basic principles and processes that provide the most effective means of controlling cross-contamination. Thorough decontamination, proper preparation and packaging, and proper loading techniques have just as much impact on the sterilization process as the sterilizer itself."