Presumed autoclave failure due to false-positive spore strip tests

Area of Science:

• Microbiology
• Sterilization Processes
• Hospital Infection Control

Background:

• Autoclaves and ethylene oxide sterilizers are critical for hospital sterilization.
• Regular spore challenge testing verifies the efficacy of sterilization processes.
• Sterilization failures can lead to significant patient safety risks.

Purpose of the Study:

• To investigate the cause of apparent sterilization failures in hospital autoclaves.
• To identify factors contributing to false positive results in spore challenge tests.
• To recommend improvements in quality control procedures for sterilization monitoring.

Main Methods:

• Sterilization processes were challenged with Bacillus species spores.
• Autoclave performance was monitored using biological indicator test strips.
• Growth medium used for spore viability testing was analyzed for contaminants.
• Quality control procedures for growth medium incubation were reviewed.

Main Results:

• Seven autoclaves showed apparent failures on 18 of 46 test strips within a two-day period.
• No mechanical, physical, or human errors were identified as the cause of autoclave failures.
• Bacillus coagulans, a contaminant, was found in the growth medium, causing turbidity at 55°C.
• This contaminant interfered with the accurate assessment of spore kill in the tests.

Conclusions:

• Contamination of growth medium with Bacillus coagulans can lead to false positive sterilization test results.
• Standard quality control incubation at 37°C may not detect this specific contaminant.
• Implementing an additional quality control incubation at 55°C for trypticase soy broth (TSB) is recommended.
• This enhanced quality control measure can prevent future misinterpretation of sterilization efficacy.