Autoclave spore strip testing has long been the gold standard for verifying proper sterilizer function.  The bacteria used are very resilient.  They require exposure to high sterilization standards to be rendered inert.  If a spore analysis shows that equipment is working properly, odds are the results are valid. However, Russ Nyberg brought up an interesting point in his recent Infection Control Today article.  Are there circumstances in which such tests can show false results?

In the case of spore indicators used in bags of regulated medical waste, perhaps so.  Experimentation revealed that when the strips were placed in biohazard bags they sometimes came in contact with chemicals that affected test results.  It is not uncommon for materials containing biocides to be mixed in with medical waste.  Disinfectant wipes are used to clean contaminated surfaces and then tossed in the biohazard bin along with everything from Petri dishes to soiled bandages.

In such an environment, bactericidal substances can come in contact with the Bacillus stearothermophilus spores used on test strips.  Such exposure can kill the spores and therefore give a negative or “no growth” result on the subsequent lab test.  This could occur whether or not fully sterile conditions were achieved throughout the rest of the load contents.

Nyberg suggests a couple of ways to deal with this problem.  One is to segregate the spore strip so it does not come into direct contact with the waste contents (or vaporized biocides in the steam).  It would then presumably deliver valid testing results.  His other advice is to perform autoclaving at a cycle level designed to achieve log-6 spore reduction rather than log-4.  It certainly doesn’t hurt to be on the safe side when handling these hazardous materials.

More Information on Biological Monitoring

The Centers for Disease Control recommends weekly verification of proper equipment functioning via biological monitoring.  The possible false negative problems outlined above don’t apply to this type of testing.  The bio-indicator sample can simply be placed in the autoclave with no other materials present to contaminate it.

These spore strips can be purchased on an auto-refill program so end users never miss a scheduled test.  This makes it easy to keep logs up to date at all times.  Third party testing companies provide both the supplies and the pass/fail results for accurate record keeping.  If no spores survive the sterilization process, the subsequent incubation at the third party lab will show no cell multiplication.  This is an excellent indicator that the autoclave is performing to the desired standard.

Of course, this is not a replacement for regularly scheduled maintenance.  Sterilizers need to work correctly during every load to ensure patient safety.  Valves and seals can deteriorate over time causing a loss of pressure and inadequate steam penetration. These should be checked regularly and replaced as necessary.  If your equipment is reaching the end of its life span and you are making a decision to purchase a new unit, click here for our free report.  A few minutes of your time can save thousands of dollars, so get the information you need.

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