How do you know if the treated item is sterilized or disinfected? Hygienists, infection control officers, and waste managers employ administrative controls (keeping track of treatment history), formal physical tests, and operating procedures established by experience and industry standards and audited periodically.
Heat treatment processes often use a "time and temperature" criteria. These rest on laboratory validation of the effectiveness of the treatment. In the validation process samples of waste are subjected to a temperature for a given time (and sometimes with a certain oxygen content in the atmosphere.) If analysis of the samples treated in the laboratory this way shows it is safe for disposal, the operating conditions – residence time and temperature – regulators write these conditions into the operating permit and the conditions become a target for the operators of the treatment.
The second and more rigorous treatment validation is the spore test.
Biological indicators are preparations of specific microorganisms (usually bacteria) that have a known survival/die response to a sterilization processes. These indicators are used to determine the level of performance of sterilization equipment and to establish sterilization has likely occurred.
Biological indicators can be used to ensure that products are sterile in their final containers. They also are employed to ensure the sterilization of materials and equipment that are used in aseptic processing. They can also be used as a means of evaluating autoclave sterilization cycles and the quality of processes employed to decontaminate aseptic clean-room environments or isolators.
Spore-forming bacteria are the microbes most often used as biological indicators, as these microorganisms are hardier and resist sterilization better than most microflora. One form of biological indicator involves addition of spores to a carrier; a package encompasses the carrier to maintain shape. Another form is a biological indicator that includes a spore suspension inoculated into or on a representative unit of the material that is meant to be sterilized.
Sterilizer monitoring spore strips are a widely used type of biological indicators. They contain Bacillus atrophaeus, Bacillus pumilus, and Geobacillus stearothermophilus and can be used to determine whether these highly-resistant microorganisms have survived the sterilization process and therefore is the process is working as intended. A spore strip is placed in an autoclave together with the materials that are meant to be sterilized. At the end of the sterilization cycle the strip shows whether the microbes can reproduce. If the spores are unable to reproduce, a successful sterilization is achieved.
Waste management engineers employ the concept of a process challenge device (PCD). These devices are designed to be a stand-in for a larger sterilization system. The PCD is a small and disposable device that acts as a canary in a coal mine. It is overly sensitive. If the PCD shows microorganisms can survive, it means the larger unit may not be up to snuff.
PCDs are placed in the sterilizers in the place that provides the greatest challenge to sterilant penetration. PCDs play an important role in the monitoring of sterilization processes. When spores are killed in a test pack that corresponds to the greatest challenge to the process, it can be inferred that the other items in the load were likely sterilized.
Monitoring spore strips are typically sold in packs. The price for a pack of 100 spore strips is usually between $200-$600. The size of a spore strip also varies, typically ranging between 4 and 8 inches.
Biological indicators are currently the most effective way of assessing whether an environment is sterile or not. It is likely that in the near future enzyme indicators will replace biological indicators, as they are thought to provide a higher level of accuracy.