8.3 Sterilization Monitoring, Spore Testing & Failure Response

Sterilization Monitoring: Mechanical, Chemical, and Biological Indicators

Quick Answer: Sterilization assurance uses three complementary forms of monitoring. Check mechanical time, temperature, and pressure for every cycle; use chemical indicators on the outside and inside of packages; and run a biological indicator (spore test) at least weekly for each sterilizer and in every load containing an implantable item. A single positive steam-sterilizer spore test requires removing the sterilizer from service, reviewing procedures, quarantining implantables, and repeating the test. If mechanical and chemical indicators were acceptable, nonimplantable items do not automatically require recall after one isolated positive result.

No indicator works alone. A gauge can show the chamber reached a temperature without proving the sterilant penetrated a package. A chemical indicator can show exposure to selected variables without proving microbial kill. A biological indicator provides the most direct challenge to the process but does not replace cycle-by-cycle checks.

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1. The Three Monitoring Layers

External Class 1 process indicators distinguish processed from unprocessed packages. Internal multivariable indicators help show that sterilizing conditions reached the inside. A Bowie-Dick test is a specific air-removal test for a dynamic-air-removal steam sterilizer and is not a substitute for the routine biological indicator.

The biological indicator organism must match the sterilization method. Geobacillus stearothermophilus is used for steam and unsaturated chemical-vapor sterilizers. Bacillus atrophaeus is used for dry heat and ethylene oxide. Follow the sterilizer and indicator manufacturers’ instructions because placement, incubation, cycle selection, and interpretation are device-specific.

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2. Running and Interpreting a Spore Test

Place the test indicator in the area of the chamber considered most difficult for the sterilant to reach, as directed by the manufacturer or process-challenge-device instructions. Process it using the selected cycle. Incubate it with an unprocessed control from the same lot.

• The processed test indicator should be negative, showing that the challenge spores were killed.
• The unprocessed control should be positive, showing that the spores were viable and the incubation system could detect growth.
• A negative control makes the run invalid; repeat the test with a valid control.
• Record the sterilizer, cycle or load number, date, operator, indicator lot and expiration, results, and any corrective action.

A negative biological indicator supports that the monitored process was effective, but package integrity and handling still matter. A wet, torn, punctured, or opened package is contaminated by an event even if its original cycle passed.

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3. Current CDC Response to a Positive Steam BI

Use a stepwise response rather than assuming every item since the last negative test is automatically nonsterile:

1. Take the sterilizer out of service. Notify the responsible person and do not run patient-care loads.
2. Review the evidence. Check mechanical records, internal and external chemical indicators, loading, packaging, cycle selection, water supply, and BI handling for operator or equipment error.
3. Protect implantables. Recall and quarantine implantable items from the suspect load and do not use them until sterility is demonstrated.
4. Repeat the BI promptly using the same cycle that produced the positive result and correct any identified operating error. Follow the dental CDC procedure and the manufacturer’s instructions.
5. If the repeat test is negative and operating procedures were correct, the sterilizer may return to service under the applicable protocol. If repeat testing remains positive, keep the unit out of service, arrange inspection or repair, and requalify it with the required consecutive negative challenge cycles.
6. When a malfunction or defective procedure is confirmed, or repeated tests remain positive, recall items processed since the last acceptable negative BI when possible, rewrap, and reprocess them in a functioning sterilizer.

For a single positive steam BI with acceptable mechanical and chemical indicators, CDC states that nonimplantable objects do not necessarily require recall unless the sterilizer or procedure is defective. This distinction prevents an isolated laboratory or indicator anomaly from being treated as proven failure while still protecting patients through immediate investigation and repeat testing. Follow more conservative manufacturer, facility, state, or method-specific requirements when they apply.

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4. Storage and Documentation

Sterility is event-related. Store processed packages in clean, dry, enclosed storage and inspect the seal and wrapper before use. Reprocess a package that is wet, torn, punctured, opened, dropped into contamination, or otherwise compromised. Rotate stock, but do not treat an arbitrary calendar date as proof that an intact package became contaminated unless the package system or jurisdiction specifies a shelf life.

A complete log links a patient-care item to the evidence for its cycle. Record the load identifier, contents, mechanical parameters, chemical results, BI result when applicable, operator, and maintenance or failure response. Retain records for the period required by state or local regulation and facility policy.

[!CAUTION] A color change is not proof of sterility. Chemical indicators show exposure to specified variables; only the combined monitoring program supports release of a load.

[!IMPORTANT] Implantable items receive extra protection. Include a BI in every implant load and quarantine the implant until the BI is negative whenever possible.