Failed Steam Sterilization BI: Next Steps

When a biological indicator (BI) shows a failed steam sterilization cycle, the immediate action is to remove the load from service, quarantine all items processed in that cycle, and do not use them until the cause is identified and corrected. You must then investigate the likely causes, re-run the sterilization cycle with a new BI after making corrections, and document the entire event and corrective actions per your facility’s protocols.

Understanding Biological Indicators

Biological indicators are the most stringent form of sterilization monitoring because they directly test whether the sterilization process killed highly resistant microorganisms. They contain a known population of bacterial spores—typically Geobacillus stearothermophilus for steam cycles—that are far more resistant to heat than typical pathogens. If the spores are killed, the cycle is considered effective; if they survive, the cycle has failed to achieve sterility assurance.

BIs come in two main formats: self-contained vials with the spore strip and growth medium in one unit, and spore strips that must be transferred to growth medium after the cycle. Both require incubation at a specific temperature (usually 55–60°C for steam) and observation for a color change or pH shift that indicates bacterial growth.

Immediate Response to a Positive BI

The first step is to contain the situation. Do not reprocess or use any items from the failed load. Follow these steps in order:

• Remove the entire load from service and quarantine it in a clearly labeled area.
• Notify the infection control team, sterilization supervisor, and any other designated personnel according to your facility’s policy.
• Do not release any items from that load for patient use until the investigation is complete and the load is cleared or reprocessed.
• Record the BI lot number, cycle number, date, time, and the operator’s name on the sterilization log.
• If the BI was a spore strip, ensure it was transferred to growth medium correctly and incubated at the proper temperature; a false positive can occur if the medium is contaminated or the incubation temperature is wrong.

Investigating the Root Cause

Once the load is quarantined, systematically review every variable that could affect sterilization. The most common causes of a positive BI in a steam sterilizer are:

• Incomplete air removal: Air pockets prevent steam from contacting the load, leaving areas below sterilization temperature. Check the vacuum pump, air detector, and chamber drain.
• Incorrect temperature or time: Verify the cycle parameters against the manufacturer’s instructions. A temperature that is too low or a holding time that is too short will not kill spores.
• Overloading or improper loading: Dense or tightly packed loads can block steam penetration. Ensure items are placed with space between them and that containers are oriented to allow steam flow.
• Wet or damp load: Excess moisture can dilute steam and reduce its lethality. Check the drying phase and steam quality.
• Mechanical failure: Faulty temperature sensors, pressure gauges, or timers can cause the cycle to run incorrectly. Review the sterilizer’s cycle printout or data logger.
• BI handling error: A positive result can occur if the BI was exposed to a contaminated environment after the cycle, or if the incubation temperature was too low, allowing the spores to grow slowly.

If the sterilizer has a chemical integrator or class 5 chemical indicator, compare its result with the BI. A chemical indicator that passes while the BI fails suggests a problem with the BI itself or with steam penetration to that specific location.

Corrective Action and Retesting

After identifying and correcting the likely cause, you must re-run the sterilization cycle with a new BI to verify that the problem is resolved. Do not use the original load for patient care until it has been reprocessed through a successful cycle. The steps are:

1. Correct the identified issue (e.g., adjust loading, repair the sterilizer, or change the cycle parameters).
2. Place a new BI in the same location in the chamber where the original positive BI was placed, if possible, or in the most challenging location for steam penetration.
3. Run a complete sterilization cycle with the same parameters as the failed cycle.
4. Incubate the new BI and confirm a negative result (no growth) after the recommended incubation period (usually 24–48 hours for steam).
5. If the new BI is negative, the sterilizer is considered functional, and the reprocessed load can be released after verifying all other monitoring (chemical and physical) is within limits.
6. If the new BI is positive, the sterilizer must be taken out of service and serviced by a qualified technician before any further use.

Document all corrective actions, the retest results, and the final disposition of the load. This record is essential for quality assurance and regulatory compliance.

When to Call for Service

If the retest BI is positive, or if you cannot identify a clear cause for the initial failure, the sterilizer should be taken out of service immediately. Contact the manufacturer’s service department or a certified biomedical technician. Do not attempt to operate a sterilizer that has failed a biological test, as this could lead to serious patient infections. While waiting for service, you may need to use an alternate sterilizer or send items to another facility for reprocessing.

Preventing Future Failures

Routine maintenance and proper use are the best defenses against BI failures. Follow these practices:

• Perform daily cleaning of the chamber, door gasket, and drain strainer.
• Run a biological indicator at least weekly, and preferably every load that contains implantable devices.
• Use a test pack that is representative of the most difficult-to-sterilize items in your facility.
• Ensure all staff are trained on proper loading, cycle selection, and BI placement.
• Keep a log of all BI results and review them for trends—a sudden increase in failures may indicate a developing mechanical problem.

Frequently Asked Questions

Can I use a chemical indicator instead of a biological indicator to release a load? No. Chemical indicators (class 1–6) only show that certain conditions were met (e.g., temperature, time), but they do not prove that spores were killed. Biological indicators are the only monitoring method that directly tests microbial lethality. For implantable devices, a BI is required for every load.

How long should I incubate a BI before reading it? For steam sterilization, most self-contained BIs require 24 hours of incubation at 55–60°C. Some rapid-readout BIs can give a result in 1–3 hours using an enzyme-based detection system, but these must be confirmed with a 48-hour culture if the rapid result is positive. Always follow the manufacturer’s instructions for the specific BI you use.

What if the BI is positive but the chemical indicators all passed? This is a red flag that the BI may have been placed in a location that did not receive adequate steam penetration, or that the chemical indicators are not sensitive enough. Do not ignore a positive BI. Investigate the load configuration and consider running a Bowie-Dick test to check for air removal.

Can a false positive BI happen? Yes, but it is rare. False positives can occur if the BI is contaminated after the cycle (e.g., during handling), if the growth medium is contaminated, or if the incubation temperature is too low. To minimize this, use aseptic technique when handling BIs and verify the incubator temperature with a calibrated thermometer.

What should I do with the items from the failed load? They must be reprocessed through a complete, successful sterilization cycle before use. If the items are heat-sensitive and cannot be reprocessed, they must be discarded. Never use items from a load that has failed a BI without reprocessing.

How often should I run a biological indicator? At a minimum, run a BI weekly, but many guidelines recommend daily for high-volume sterilizers. For every load containing implantable devices, a BI must be included. Always follow your facility’s policies and regulatory requirements.

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