Sterilization is a process that is intended to destroy viable forms of microbial life including bacteria, molds, yeasts, viruses, protozoa, and algae (including bacterial spores) to an acceptable sterility assurance level (SAL). SALs were first used in the food canning industry and refer to the degree to which an item is expected to be non-sterile after exposure to a sterilization process. While we use phrases like “terminal sterilization,” we must remember that sterilization is a matter of degree or probability. In a sterilization process, the nature of microbiological death is therefore described by an exponential function, an expression of probability.
For instance, a SAL of 10-6 means that there is a one in a million chance (probability) that a microorganism will remain after the sterilization process. However, while this probability can be reduced to a very low number, it can never be reduced to zero. ANSI/AAMI ST67:2003 contains a decision tree to be used to determine the SAL for medical devices to be terminally sterilized.
Sterilization is necessary when microorganisms are a contaminant. Such cases would include surgery, the implantation of medical devices, or the injection of solutions into the body. Sometimes, the device, instrument, or solution can be sterilized and packaged until it is ready for use. Often, however, sterilization, regardless of method, has a deleterious effect on the product. In such cases, the alternative is asepsis, the prevention of contact with microorganisms. Aseptic processing or manufacturing generally requires the use of a cleanroom and cleanroom apparel. A sterile cleanroom is often called a sterile suite or aseptic cleanroom. These rooms are meticulously maintained in a sterile condition by rigorous housekeeping and special decontamination procedures governed by the FDA and detailed in the Federal Guidelines to Good Manufacturing Practice (GMP). Note: If you see cGMP, the small case “c” stands for “current.”
Cleanroom garments used in aseptic cleanrooms must be sterile. ANSI/AAMI ST67:2003 identifies the sterility assurance levels for terminally sterilized products. Many companies manufacturing products in an aseptic clean-room require all components used in aseptic processing, including cleanroom garments, to be terminally sterilized to 10-6SAL.
There are three typical methods of sterilizing clean-room garments: steam autoclaving, ethylene oxide (EtO), and ionizing radiation (gamma or electron beam). While each has advantages and disadvantages, gamma irradiation is the most popular method used today.