Why Do We Use a Control BI in Steam Sterilization Quality Assurance Monitoring?
Why does sterilization monitoring include both a biological indicator ‘test’ and a ‘control’? Post incubation is it not clear enough that the user will simply look to see if the vial is purple or yellow? Seems simple to observe a color change and log the outcomes. This is all indeed true, however, dental professionals need to remember the structure of scientific testing and validating. Going back to high school science and the science labs in undergrad we were all taught the purpose of following the scientific method. As we get busy in our typical days in a dental clinic, we may not be stopping to think that every day we are conducting a scientific experiment to conclude an evidenced-based outcome. Applying the scientific method to biological indicator (BI) testing in steam sterilization derives the answer to the question of why we need both a ‘test’ and a ‘control’ BI from the same Lot number.
The control in an experiment or validation test, such as using a control BI for steam sterilization, serves as a baseline for comparison to ensure the process's reliability. In this context, the control verifies that Geobacillus stearothermophilus spores in the BI vial remain viable when not exposed to sterilization conditions. This confirms that any spore inactivation in the test BI is directly attributable to the sterilization process rather than external factors, such as improper storage conditions, exposure to incorrect temperatures, proximity to the sterilizer, expired vials, or tampering. To maintain accuracy and reliability, both the test and control BIs must come from the same lot number.
Scientific methodology involves structured testing with BI’s to verify sterilization efficacy. As stated above, the control BI acts as a baseline, ensuring reproducibility and accurate results. Additionally, variable isolation is critical: the independent variable encompasses sterilization parameters like temperature, pressure, and exposure time, while the dependent variable is the presence or absence of microbial growth in the test BI. The unprocessed control BI should exhibit microbial growth to confirm the spores' initial viability and provide a valid comparison with the test BI.
The following is an overview of a BI in its application within the Scientific Method:
- Definition of Control A control BI is a baseline condition in the validation process that is not exposed to the independent variable. The control BI vial’s spores have not been subjected to sterilization conditions. This control verifies the spores' viability under normal conditions.
- Purpose of a Control in Steam Sterilization
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Baseline Comparison: Confirms the sterility process by comparing the control BI (viable spores) with the test BI (exposed spores). The colour change signals the sterilization outcome:
- A negative BI (indicating no microbial growth and successful sterilization) remains purple.
- A positive BI (indicating microbial growth and a sterilization failure) turns yellow.
- Elimination of Alternate Explanations: Ensures that sterilization efficacy is solely due to the steam process, ruling out external factors like storage issues or faulty indicators.
- Verification of Test Validity: Demonstrates that the BI system functions as intended, as the control BI must show microbial growth if the spores are viable.
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Baseline Comparison: Confirms the sterility process by comparing the control BI (viable spores) with the test BI (exposed spores). The colour change signals the sterilization outcome:
- Significance of Using a Test Control
- Establishes a cause-and-effect relationship between sterilization conditions and spore inactivation.
- Increases the process’s validity and reliability by confirming that test results are accurate.
- Differentiates between effective sterilization and potential equipment failures or errors in sterilization parameters.
In conclusion, the discussion can be framed with risk management. Using a test and control BI together enhances the reliability and validation of steam sterilization protocols, ensuring patient safety and compliance with regulatory standards.
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Michelle Aubé (Simmonds) RDH, maxill Dental Hygiene Educator
Michelle is a Dental Hygiene Speaker, Consultant and Educator with over 30 years of experience as a RDH and 4 years as a CDA. She is a professor and curriculum writer at Fanshawe College in both the dental hygiene and continuing education program sharing her knowledge in IPAC, professional practice, periodontal classification, social justice, advocacy and clinical applications. She is maxill's CE and IPAC Director and wears various IPAC hats including auditing federal correctional facilities dental clinics for IPAC standards. Michelle is ODHA's Regional Board Director and authors articles for CDHA's OH Canada professional publication and continues to practice clinically in London ON. She is a CDHO IPAC Remedial Facilitator and IPAC Expert Opinion. Her strong ethics has allowed her to serve on the Discipline Committee at Algonquin College and hold the position of a CDHO Quality Assurance Assessor for 7 years. As a lifelong learner she is completing a BA in Adult Education at Brock University. Her diverse dental background and current status as a practicing RDH offer a fulsome and realistic view of dental-related topics. As a passionate champion for the profession, she advocates for equity, professional autonomy, and systemic change, true grassroots leadership at its finest.
Michelle can be reached at michellea@maxill.com
