After a Failed Spore Test: Quarantine, Retest and Release in a Canadian Clinic
A positive spore test is not a sterilizer problem at first. It is a records problem, because what happens in the next four hours decides whether the event is a controlled corrective action or a week of packs that nobody can vouch for.
Clinics that handle this well have one advantage: the response is already written down, and the staff have practised it once. Clinics that handle it badly usually have a good sterilizer and no procedure, which means the first hour is spent arguing about whether the test strip itself was faulty.
Why should you confirm the test before you condemn the cycle?
Biological indicators are not infallible, and neither are incubators. The first check is the test system around the result: the incubation temperature and time, the lot and expiry of the 1-hour rapid readout indicators in use, storage conditions before use, and the positive control that should have turned positive in the same run.
ISO 11138-1 and ISO 11138-3 describe what a biological indicator is required to do, including the population and resistance characteristics that make the result meaningful. A test strip left in a warm room, or read six hours late, is not a valid test of the cycle. A positive control that fails tells you the incubator or the media is at fault, and the whole run is void.
Which loads go on hold, and for how long?
Quarantine is where clinics lose confidence, so make it mechanical. Define the window by records rather than by memory: every load released since the last documented negative result for that sterilizer goes on hold. Packs stay labelled, go into a marked area, and are not used.
Traceability decides how wide the hold is. A clinic that records room, operator and load number can hold precisely the affected packs. A clinic that records only a date has to hold everything from that date, and may have to recall instruments already in a drawer upstairs. The first case costs an awkward afternoon; the second costs credibility.
How do you find the cause with the load in front of you?
Most failures come from a short list, and the load itself usually shows which one applies. Open the chamber, look at the packs from the failing cycle, and read the pattern before touching the machine.
| What you see | Likely cause | Next action |
|---|---|---|
| Wet packs, heavy condensation | Air removal or drying fault | Check drain, filters, door seal; service call |
| Indicator light in the centre of the load | Load too dense or badly arranged | Re-arrange, re-test with a load challenge |
| Indicator light on every pack | Cycle parameter or steam quality | Review cycle log, water quality and supply pressure |
| Seal lifted or pack blown | Overfilled pouch or bad seal | Review fill limits and sealer settings |
| Test fine, control positive | Indicator storage or incubator fault | Re-run with new lot, verify incubator temperature |
| Repeated failures after service | Mechanical or installation issue | Escalate to the service provider with records |
The load pattern is evidence, so photograph it before the tray is dismantled. A service technician who arrives with a photograph and a cycle log finds the fault faster than one who arrives with a description.
What can staff fix, and what needs a service call?
Operator-level correctives are limited and worth doing immediately: re-arrange the load, choose the correct cycle, check that pouches are not overfilled, confirm the door seal is clean and seated, confirm the chamber drain strainer is clear. Anything involving a valve, a controller, a pressure transducer or a calibration is a service item.
Do not restart production to test a hypothesis on live instruments. Run the clearing cycles empty or with a standard load challenge, log them, and only release the sterilizer when the sequence is complete.
How many consecutive negative cycles clear the sterilizer?
The accepted path in most Canadian programs is three consecutive negative cycles, each with its own chemical indicator, biological indicator and record. The chemical indicators specified under ISO 11140-1 and used according to the guidance in ISO 15882 tell you that conditions were reached inside each pack. The biological indicator tells you the cycle killed spores.
Both signals stay in the folder. A clearing sequence documented with only chemical indicators is weaker evidence, and it is the first thing an experienced reviewer will ask about.
How are quarantined items returned to use?
Quarantined instruments are not returned to the shelf. They are inspected, cleaned if soiled, re-packaged in new pouches, and processed as fresh loads with new indicators. A pack that has been through two cycles and then stored is a pack whose history nobody can reconstruct.
This is also the moment to check packaging stock. A clinic that ran out of the right pouch size and started overfilling is a clinic that will fail again next month. The Class 4 self-sealing pouch range covers 16 size variants for exactly this reason, and the indicator tape closes wrapped sets when a tray is too large for any pouch.
What has to change so it does not happen again?
Weekly spore testing is the floor in most dental and clinic settings, with daily chemical and physical monitoring and a Bowie-Dick test at the start of a day in which the sterilizer has been off, serviced or moved. Frequency is set by provincial guidance and by the sterilizer manufacturer's instructions, and both should be quoted in the clinic SOP.
Where the failure came from load design, add a load challenge to the weekly routine: a small pack placed in the coldest part of the chamber. Where it came from water quality, add a test interval for feed water. Where it came from packaging, re-run the fit test. Each corrective action should change one line in the procedure, not live only in the incident report.
What does the incubator have to do with it?
A spore test is only as good as the incubation conditions. The 1-hour rapid readout indicators need a dry block at the temperature their instructions specify, held within a narrow band for the full readout period, and the 24-hour self-contained indicators need a stable 24 hours at their own set point.
That is a job for a dry block incubator with a digital set point and a lid, not for a warm cupboard. Both indicator formats and the incubators that run them sit in the sterilization monitoring range, together with the logs that make the schedule visible.
How do you record the event so it stands up?
One folder per event, in this order: the failing result with lot number and read time, the incubator temperature record, the list of held loads, the inspection findings, the cause, the corrective action, the three clearing cycles, the release signature and the date. Keep it for the same period as the sterilization records themselves.
The point is not paperwork for its own sake. A documented response is what converts an alarming afternoon into a controlled event, and it is the difference between a clinic that can answer a patient question in one phone call and one that cannot answer it at all.
References
- ISO 11138-1:2017 — Biological indicators, Part 1: general requirements (checked 22 October 2026)
- ISO 11138-3:2017 — Biological indicators, Part 3: indicators for moist heat (checked 22 October 2026)
- ISO 11140-1:2014 — Chemical indicators, Part 1: general requirements (checked 22 October 2026)
- ISO 15882:2008 — Chemical indicators, guidance for selection, use and interpretation (checked 22 October 2026)
- ISO 17665-1:2006 — Moist heat sterilization, Part 1 (checked 22 October 2026)
- ISO 11737-1:2018 — Microbiological methods, Part 1: bioburden (checked 22 October 2026)
- ISO 11737-2:2019 — Microbiological methods, Part 2: sterility testing (checked 22 October 2026)
- ISO 14971:2019 — Application of risk management to medical devices (checked 22 October 2026)
- ISO 13485:2016 — Medical devices, quality management systems (checked 22 October 2026)
- ISO 15223-1:2021 — Symbols to be used with medical device labels (checked 22 October 2026)
- ISO 11607-1:2019 — Packaging for terminally sterilized medical devices (checked 22 October 2026)
- ISO 11135:2014 — Ethylene oxide sterilization of health care products (checked 22 October 2026)
- ANSI/AAMI ST79:2017/(R)2022 — Comprehensive guide to steam sterilization (checked 22 October 2026)
- Infection Prevention and Control (checked 22 October 2026)
- Infection Prevention and Control (checked 22 October 2026)
Keep the response on paper: download the printable failed-load response SOP template and fill in your own names, incubator settings and hold points before you need it.
Count your weekly spore tests with the sterilization usage calculator, ask a compliance specialist to review a failure, or price indicator and incubator quantities on the bulk quote form, and facility accounts can use wholesale ordering for facilities. Reselling? become a distributor.
Not sure how this applies to your own setup? Ask a sterilization compliance specialist — you’ll get a written answer specific to your equipment and province, with the regulation or standard cited.
Related Reading
- Biological indicator incubator care: the daily routine
- Storage, shelf life and lot tracking for biological indicators
- Autoclave load configuration: arranging packs and trays
Frequently Asked Questions
What is the first thing to do when a spore test is positive?
Stop releasing loads from that sterilizer. Verify the test itself before you condemn the machine: check that the incubator held the right temperature, that the indicator was inside its expiry date, that the reading was taken at the correct time, and that the positive control behaved as expected. A control that fails means the result cannot be trusted either way.
Which loads have to be quarantined?
In practice, every load processed since the last documented negative result for that sterilizer, which is why good sites never let the gap between records run long. Pull the packs, keep them identifiable, and do not use the instruments until the sterilizer has been cleared. Some sites extend the hold to items already in storage if traceability is weak.
Can I repeat the test on the same load?
You repeat the test on the sterilizer, not on the packs. Re-processing a load that was already processed once adds another cycle to the instruments and does not answer whether the first cycle worked. The usual sequence is to correct the cause, run three consecutive negative cycles, then reprocess the quarantined items as fresh loads with new packaging.
How many consecutive negative cycles clear the sterilizer?
Three is the number most Canadian programs and AAMI ST79 users work to, with each cycle carrying its own chemical indicator, biological indicator and record. Some sites use a shorter path after a clearly identified operator error, but that decision belongs in the written procedure and should be supported by a risk assessment rather than decided at the bench.
What causes a positive biological indicator?
The usual list is short: a load that was too dense or wrongly arranged, packaging that blocked steam, an air removal fault, a door seal leak, water quality that produced scale or carryover, an operator choosing the wrong cycle, or an incubator that ran cool. The indicator itself is rarely the cause, but expired or badly stored indicators belong on the list until they are ruled out.
Do I need to tell anyone outside the clinic?
Follow your provincial guidance and your own adverse event procedure. If patients were exposed to instruments from a load that could not be validated, the clinical lead decides what disclosure is required, and that decision is documented. In most small clinics the first external conversation is with the sterilizer service provider and the infection control contact for the region.
What does a failed spore test cost?
More than the test strip. Expect instrument downtime, rescheduled appointments, replacement packaging and staff time for the investigation, plus the service call if a mechanical fault is found. That is why the spore test schedule is a cost control measure: catching a drifting cycle early costs less than recalling a week of packs from the shelf.
How do I prove the response was done properly?
Keep one folder per event: the failing result, the incubator and lot details, the quarantine list, the cause identified, the corrective action, the three clearing cycles with their results, and the release sign-off. ISO 13485's process thinking and ISO 14971's risk file logic both point the same way, and auditors read the folder rather than the story.
Last updated: October 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334).
0 commentaire