New ANSI/AAMI Standard Transforms Ethylene Oxide Sterilization in Health Care

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Recently, the Association for the Advancement of Medical Instrumentation (AAMI)/American National Standards Institute (ANSI) released an update on ethylene oxide (EO) sterilizers called “ANSI/AAMI ST24:2024 General-purpose ethylene oxide sterilizers with automated process control and ethylene oxide sterilant sources intended for use in health care facilities.”

According to the press release, ANSI/AAMI ST24 outlines the labeling, safety, performance, and testing requirements for ethylene oxide sterilizers used in health care facilities with automatic controls. The revised standard is crucial for medical device manufacturers and sterile processing departments (SPDs) in hospitals, clinics, and laboratories, particularly amid supply chain challenges and regulatory changes due to the Environmental Protection Agency’s (EPA's) new Final Rule on EO.

For details of this update's changes, Infection Control Today^® (ICT^®) asked A.E. (Ted) May, president and CEO of the Andersen Products Division of Andersen Sterilizers, a North Carolina-based medical device manufacturer specializing in low-temperature sterilization equipment and hospital consumables. He has over 20 years of experience in infection control and is an expert on ethylene oxide sterilization, with particular expertise in EO flexible chamber systems.

He is a cleared advisor to the US Federal International Trade Advisory Committee on medical devices (ITAC3), where he is cochair of the Life Sciences Subcommittee. Ted serves on several AAMI committees, including as the current cochair of the Hospital Ethylene Oxide (EO) Sterilizer Working Group (WG63). He has also been a subject matter expert for the US delegation to the international ISO Ethylene Oxide Working Group (ISO TC198 WG1).

ICT: What motivated the update of the ANSI/AAMI ST24 standard after 2 decades, and what were the primary objectives you aimed to achieve with this revision?

A.E. (Ted) May: Medical device technology advances rapidly. This includes the technologies available for device sterilization and disinfection. It has been over 20 years since the third edition of ANSI/AAMI ST24 was published. During this period, ethylene oxide (EO) use in health care facilities has changed significantly. This fourth edition of ANSI/AAMI ST24 has been revised to include newly developed EO sterilization systems that the FDA has cleared since the last edition was published and were not adequately described in the previous edition of the standard. Our goal with this latest revision was to better reflect the current ethylene oxide sterilization technologies available to health care facilities.

ICT: Can you elaborate on the significant changes and advancements in ethylene oxide (EO) sterilization technology incorporated into the new edition of ANSI/AAMI ST24?

AEM: Many people believe that EO sterilization technology is a "settled science" that has not progressed much since the end of the 20th Century. This is not true. When the last version of ST24 was published in 2005, the typical EO sterilizer was a large, wall-mounted chamber system running off 50-lb gas tanks. These systems were often installed in dedicated rooms with separate areas for product aeration and tank storage. They used a large amount of gas and took up a significant amount of space.

In the last 10 years, the Food and Drug Administration (FDA) has cleared much smaller tabletop EO sterilizers that employ a new high-efficiency flexible chamber design. These EO flexible chamber systems use a minimal amount of gas, about 17 grams per cycle, and have replaced large EO tanks with single-use cartridges. Equally important to the managers of cramped SPDs, these EO flexible chamber sterilizers are self-contained units that do not require the external air compressors and water lines of previous EO systems.

ICT: How does the updated standard address the challenges faced by the medical device industry, particularly considering the Environmental Protection Agency’s (EPA’s) new Final Rule concerning EO?

AEM: The EPA’s recent rule focused mainly on large, contract sterilization facilities using many tons of EO each year. These facilities are now looking for ways to reduce their gas usage. EO remains the most popular sterilization method for new medical devices because of its broad material compatibility and proven reliability. Health care facilities must be aware that they have high-efficiency EO options that are both FDA-cleared and recognized in AAMI guidance.

Also, since 2008, the EPA has required that all EO sterilizers in health care settings accomplish sterilization and aeration in the same chamber to avoid potential worker exposure during off-gassing. This requirement was repeated in the recent EPA guidance. These so-called "all-in-one” systems were not available when the last version of ST24 was published.

ICT: What are the key requirements for labeling, performance, safety, and installation for EO emission control systems as outlined in the revised ANSI/AAMI ST24?

AEM: Key requirements have not changed. All EO sterilant containers must be labeled in accordance with US Department of Transportation and EPA regulations. Performance, safety, and installation requirements must still meet all applicable local, state, and federal regulations, as well as manufacturer’s instructions.

ICT: How does the updated standard improve worker safety, particularly concerning thermal hazards, air filtration, and exposure monitoring in health care facilities using EO sterilization?

AEM: The prevention of worker exposure and monitoring of EO is referred to in the Occupational Safety and Health Administration guidance: 29 CFR Part 1910.1047 2007 Toxic Hazards and Substances-Ethylene Oxide and NESHAP 40 CFR Part 63 2007.

EPA is expected to release new guidance on health care worker safety concerning EO, but this has not been released yet. Testing for thermal hazards with traditional EO systems has not changed. However, flexible chamber sterilizers do not present the thermal hazards that are possible with earlier chamber designs, so this testing is optional for these systems.

ICT: Can you discuss the importance of the new test methods and procedures included in the standard and how they contribute to demonstrating conformance with ANSI/AAMI ST24?

AEM: Test methods for traditional chamber-type EO sterilizers remain the same. However, due to design differences, test methods for EO flexible chamber systems have become simpler. For example, EO flexible chamber sterilizers operate at atmospheric pressure and do not employ a vacuum cycle, so pressure requirements and chamber corrosion resistance are irrelevant to these systems. Likewise, flexible chamber sterilizers do not present the thermal hazards possible with earlier chamber designs, so this testing is not required.

ICT: How do you see the updated ANSI/AAMI ST24 standard impacting the practices of medical device manufacturers and health care facilities regarding EO sterilization and overall patient safety?

AEM: EO sterilization remains an essential tool for health care facilities. In 2015, a carbapenem-resistant Enterobacterales outbreak linked to improperly reprocessed duodenoscopes killed dozens of patients. Amid this crisis, the FDA released 4 supplemental measures to combat the outbreak. Ethylene oxide sterilization was the only sterilization method specifically recommended by the Agency. Subsequent investigation revealed that every facility that adopted EO sterilization of their duodenoscopes ended outbreaks quickly. As reports of infections have continued, the FDA has added several other endoscope types to their recommendation for sterilization.

However, most US health care facilities no longer offer EO sterilization, largely due to concerns over the earlier, large EO chamber/tank systems. Infection control professionals must be aware that modern, high-efficiency EO systems are available to assist in their fight against the growing threat of multidrug-resistant organisms. The updated ANSI/AAMI ST24 standard should increase awareness of current EO sterilization options.