Low-temperature sterilization technologies: do we need to redefine "sterilization"?

Abstract

The provocative article by Alfa and colleagues in this issue of Infection Control and Hospital Epidemiology) should lead to a reevaluation of our current concept of sterilization. This editorial will address several important issues relevant to evaluating the new low-temperature sterilization processes. These include the factors contributing to the development of alternative technologies to the current standard of ethylene oxide with a chlorofluorocarbon (CFC) carrier; characteristics of an ideal sterilization process for use in health care; review of current low-temperature sterilization technologies using the criteria for an ideal sterilant; recommendations for testing protocols when assessing the microbiocidal efficacy of sterilants (eg, spore load, inoculated vehicle, presence of proteinaceous material); and the need to develop a standard measure of cleaning efficacy. Ethylene oxide (Et0) has been used widely as a low-temperature sterilant since the 1950s. It has been the most prevalent process for sterilizing temperatureand moisture-sensitive medical devices and supplies in healthcare institutions in the United States. Current Et0 sterilizers combine Et0 with a CFC stabilizing agent, most commonly in a ratio of 12% Et0 mixed with 88% CFC (referred to as 12/88 Et0). For several reasons, hospitals are exploring the use of new low-temperature sterilization technologies. First, CFCs are to be phased out in December 1995 under provisions of the Clean Air Act.2 CFCs were classified as a Class I substance under the Clean Air Act because of scientific evidence linking them to destruction of the earth's ozone layer. Second, some states (eg, California, New York, Michigan) require the use of Et0 abatement technology to reduce the amount of Et0 being released into ambient air by 90% to 99.9%. Third, the Occupational Safety and Health Administration regulates the acceptable apor levels of Et0 due to concerns that Et0 exposure represents an occupational hazard. These constraints have led to recent development of alternative technologies for low-temperature sterilization in the healthcare setting. Alternative technologies to Et0 with CFC include 100% EtO, Et0 with a different stabilizing gas such as carbon dioxide or hydrochlorofluorocarbons, vaporized hydrogen peroxide, gas plasmas, ozone, a d chlorine dioxide. These new technologies should be compared against the characteristics of an ideal low-temperature (<600 C) sterilant (Table 1).3 While it is apparent that all technologies will have limitations (Table 2), understanding the limitations imposed by restrictive device designs (eg, long, narrow lumens) is critical for proper application of new sterilization technology.4 For example, the development of increasingly small and complex endoscopes presents a difficult challenge for current sterilization processes. This occurs because microorganisms must be in direct contact with the sterilant for inactivation to occur. The article by Alfa and colleagues provides important data in assessing the efficacy of several low-