Sterility Assurance Levels for Terminal Sterilization of New / Emerging Healthcare Products

Background: The sterility assurance level (SAL) was first developed by the food canning industry.  In order to demonstrate sterility, since it is impossible to sample all canned items after moist heat sterilization, a safety factor was established incorporating the kinetics of inactivating bacterial spores that would give an equivalent of a 12-log spore reduction.  In the 1960’s the Swedish public health authority required a stated SAL of 10^-6 (probability of 1 viable organism per 1,000,000 products) for medical devices labeled “sterile”.  Currently SALs are used to measure sterilization process efficacy and apply to terminally-sterilized medical products.

Objective: The intent is to determine what are acceptable SALs for new / emerging health care products such as combination products (medical device with a pharmaceutical and/or biologic component), devices with materials that cannot withstand traditional terminal sterilization processes, and products that are cell-and tissue- based.

Methods: The U.S. Food and Drug’s Medical Device Reporting Program (MedWatch) was examined to determine if there is an increase in infections associated with products that are labeled “sterile” and do not have an SAL of 10^-6, such as combination products, medical devices with sterilization-sensitive materials, and products that are cell- and tissue-based.

Results: Combination products and cell-and tissue-based medical devices are relatively new on the market, so there are few reports of infections associated with these devices having an SAL of 10^-6 or other SAL (e.g., 10^-3).  In addition, there is no evidence at this time that shows conclusively that devices with an SAL of 10^-3, for example, are more likely to be linked to nosocomial infections than devices with an SAL of 10^-6.  Data indicates that the majority of nosocomial infections arise in the clinical environment due to post-sterilization handling, the environment itself, and in-use handling practices that are not aseptic.

Conclusions: As health care products continue to expand to include devices with new materials that cannot withstand traditional terminal sterilization, combination products that include pharmaceuticals and/or biologics, and cell- and tissue-based products, new sterilization methods for these products may need to incorporate a variety of SALs if these items are to be terminally sterilized, labeled “sterile”, and still function as intended for use.