What Happens When an Autoclave Spore Test Fails? A Step-by-Step Response

A positive spore test is not a paperwork problem. It means a load came out of the sterilizer without evidence that it was sterile, and every item in that load is now in question. The clinic that handles this well is not the one with the most expensive autoclave - it is the one with a written sequence it can follow before the first patient is seated.

What does a positive spore test actually tell you?

A biological indicator holds a known population of bacterial spores. For steam cycles that organism is Geobacillus stearothermophilus, grown at 55 to 60 degrees Celsius. The indicator is processed in a load, recovered, and incubated alongside an unprocessed control. If the processed indicator shows growth, spores survived.

That reading tells you two things and no more: the load is not verified sterile, and the process failed at least once. It does not tell you whether the sterilizer is failing today, because the test itself can be the source of the reading.

Step 1: Quarantine the load before anything else

Move the entire load to a labelled hold area and keep it out of circulation. Do not release it, do not re-wrap it, and do not return it to the shelf.

If any item from that load has already reached a patient, treat it as an infection prevention and control event: notify your IPAC lead and record which items went where.

Which test-side errors produce a false positive?

Before booking service, check the four things that most often produce a false positive:

• Was the indicator the right organism for the cycle? Steam and hydrogen peroxide use different spores, and a mismatch produces a meaningless result.
• Was the incubation temperature correct? Steam indicators need 55 to 60 degrees Celsius.
• Did the indicator get a warm start? Let a freshly processed indicator cool to room temperature before it goes into a hot incubator.
• Is the indicator in date, and was the lot stored as the instructions require?

How many retests before you call for service?

Run one repeat on a normal load, using a fresh indicator from a current lot such as a 24-hour self-contained biological indicator. If that is negative, document both results and review the load's packaging before returning the sterilizer to routine use. If it is positive, stop using the unit and arrange an inspection. A sterilizer that fails two biological indicators in a row should not process another patient-care load until it is serviced and re-tested clear.

What has to be written down?

If your clinic is still running spore tests only when something looks wrong, a small in-office routine is the less expensive habit: a dry-block incubator to read results in house, plus a five-pack biological indicator trial at CA $12.99 with shipping included so the whole sequence can be rehearsed before it matters. Clinics that already know their load mix usually step straight to the 25-pack of 24-hour self-contained indicators and buy pouches with a printed internal indicator alongside them.

References

1. Public Health Ontario - reprocessing of medical devices, infection prevention and control (checked 16 September 2026)
2. CSA Z314:23, Canadian medical device reprocessing standard (CSA Group) (checked 16 September 2026)
3. RCDSO infection prevention and control guideline, standards and guidelines (checked 16 September 2026)

Related Reading

• Sterilization compliance hub: monitoring, logs and provincial expectations
• Autoclave spore test FAQ: incubation time, warm start and failed results
• Dental autoclave spore testing: frequency, results log and what inspectors ask for
• Sterilization monitoring supplies and consumables for Canadian clinics
• dental clinic sterilization supplies
• free Ontario sterilization compliance log
• printable autoclave sterilization log sheet (free)

Frequently Asked Questions

Does one positive spore test mean the autoclave is broken?

Not on its own. A biological indicator is a pass-or-fail screen for that cycle, not a diagnosis of the sterilizer. Many confirmed failures trace back to how the test itself was run - an expired indicator, the wrong spore for the cycle type, incubation at the wrong temperature, or a warm start - rather than to a mechanical fault.

Can we release the load if the chemical indicator and the tape both changed colour?

No. Chemical indicators respond to heat, steam and time; they show that conditions were present, not that sterility was achieved. Only a biological indicator tests whether spores actually survived. When the BI is positive, the load stays quarantined regardless of what the external and internal chemical indicators show.

How many retests should we run before calling a service technician?

The common sequence is one repeat BI on a standard load, then a second repeat with a process challenge device placed in the most difficult part of the chamber. If either retest is positive, take the sterilizer out of service and have it inspected before it processes another patient-care load. Two positives in a row is a maintenance event, not a re-test event.

What has to be written down when a spore test fails?

Record the date and time, sterilizer identification, cycle number and programme, indicator brand, lot number and expiry, incubation start and finish, the result, the disposition of the load, and the corrective action taken. A follow-up entry should show the negative retest. Reviewers ask for the sequence, so the log has to read as one continuous story.

Last updated: September 2026. CliniEco Medical holds MDEL #35334 issued by Health Canada, and supplies clinics, long-term care homes and home-care programs across Canada.