Biological monitoring, commonly known as spore testing, represents the most direct and reliable method for confirming that a sterilization process has successfully eliminated all microbial life. This procedure involves placing a biological indicator, which contains millions of highly resistant bacterial spores (such as those from Geobacillus stearothermophilus in steam sterilizers), into the sterilizer chamber with a normal load of instruments. If the sterilization cycle is effective, the spores will be completely destroyed. When the indicator is later incubated, a successful test, or “negative” result, shows no bacterial growth, providing verifiable proof that the equipment has reached the necessary lethality.
Standard Routine Frequency Guidelines
The standard frequency for routine spore testing is set by major public health and medical device organizations to ensure a consistent baseline of quality control. The widely accepted minimum requirement is to perform a spore test on each sterilizer at least once every week the equipment is in use. This weekly testing frequency is recommended by bodies like the Centers for Disease Control and Prevention (CDC) and the Association for the Advancement of Medical Instrumentation (AAMI).
Routine testing provides an ongoing assurance that the sterilizer is consistently meeting the physical conditions required for sterilization (time, temperature, and pressure). While mechanical gauges and chemical indicators check cycle parameters, the biological test is the only one that directly measures the equipment’s ability to kill the most resilient microorganisms. Local jurisdictions may mandate a more frequent testing schedule, which always takes precedence.
A control biological indicator is placed outside the sterilizer and incubated alongside the test indicator. The control must show bacterial growth, confirming that the spores were viable before testing and that the incubation conditions were correct. The routine weekly test should be placed in the most challenging location within the sterilizer, often the coolest or least accessible area.
Mandatory Testing in Special Circumstances
Beyond the standard weekly schedule, specific events must immediately trigger a mandatory spore test, as these situations introduce a heightened risk of sterilization failure. Any time a sterilizer undergoes repair, servicing, or a major power interruption, it must be spore tested before being returned to routine use. The equipment must pass three consecutive sterilization cycles, each with a biological indicator, to prove its functionality has been restored.
Certain changes in procedure also require immediate biological monitoring to ensure the new process does not compromise the sterilization outcome. These mandatory tests include when personnel are newly trained on sterilization procedures or whenever a new type of packaging material, tray, or loading configuration is introduced. Such changes can alter steam penetration dynamics, making a verification test necessary to confirm the cycle remains effective.
The most stringent testing requirement applies to loads containing implantable medical devices, which are items that will be placed into a patient’s body. For these devices, a spore test must be included in every sterilization cycle. Ideally, the implantable item should not be used until the biological indicator from that specific cycle has been incubated and confirmed to be negative.
Interpreting Results and Required Documentation
A positive spore test, meaning the bacterial spores survived the cycle and grew during incubation, indicates a failure in the sterilization process and requires immediate, specific action. The sterilizer must be removed from service immediately to prevent further use of potentially contaminated instruments. All items processed in that load, and all loads processed since the last negative spore test, must be retrieved, quarantined, and reprocessed.
Upon receiving a positive result, the first step involves reviewing all mechanical and chemical monitoring records for that failed cycle to determine the cause, such as operator error or incorrect cycle settings. An immediate retest is then performed, and if the repeat test is also positive, the sterilizer must remain out of service for professional inspection and repair. The sterilizer cannot be used again for patient care until it has passed three consecutive biological tests.
Comprehensive documentation is a non-negotiable component of the spore testing cycle, necessary for both patient safety and legal compliance. Detailed logs must be maintained for every sterilization cycle, recording the mechanical parameters, the results of the chemical indicators, and the outcomes of all biological monitoring. Maintaining these records ensures accountability and provides a clear audit trail for the recall and reprocessing of instruments should a sterilization failure occur.