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What you need to know about antimicrobial efficacy test standards for hard surfaces

As the understanding of antimicrobial materials has improved, regulators and working groups such as the US Environmental Protection Agency (EPA) and the Organisation for Economic Co-operation and Development (OECD) have recognised that there are no standardized methods for the determination of efficacy under conditions typical of the environment under which a material is expected to be employed. This is especially the case with regard to indoor surfaces and touch points.

The OECD Working Group under the Inter-Organisation Programme for the Sound Management of Chemicals (IOMC) represents the interests of a number of countries and regions. It has proposed a tiered system approach1 with Tier One test methods providing proof of principle and Tier Two methods more closely representing in-use environmental conditions.

Tier One testing

Tier One tests are adequately covered by standards such as BS EN ISO 22196: Measurement of antibacterial activity on plastics and other non-porous surfaces. This establishes the basic effectiveness of a material under warm, damp conditions: 37oC and >90% humidity over a period of 24 hours. This, and the Japanese Industrial Standard on which it is predicated (JIS Z 2801), is the basis on which most early technical and marketing claims were made and often persist in promotional literature. This is now seen as inappropriate, or possibly dangerous, in that efficacy under the test conditions has been shown2 not to persist under typical indoor settings where humidity is often 50% and temperatures only 22 – 25oC.

Tier Two testing

Tier Two tests are still in the committee stage of various Standards Organisations and the OECD recommends a pragmatic, best practice approach to test protocols while new standards are under development. The development of appropriate Tier Two test standards will enable better  comparisons and the wider implementation of these technologies.

Antimicrobial Copper testing

Through dialogue with the EPA, a set of three Tier Two methods was established based upon existing tests for liquid disinfectants designed to be applied to hard surfaces. In particular, pre-drying or inocula on tes coupons and a 2 hour assessment period are recommended.  Its development included extensive discussions with experts in the infection control community, including the Association for Professionals in Infection Control and Epidemiology (APIC) and the American Society for Healthcare Environmental Services (ASHES).

See Laboratory Testing for details of the three EPA tests.

The table below compares the conditions of the Tier Two  'Efficacy as a Sanitizer' EPA test with the Tier One JIS Z 2801 (ISO 22196).

 

Table comparing conditions of EPA Self-Sanitezer test with JIS Z 2801 (ISO 22196)

 

Industry best practice antimicrobial efficacy test

The US EPA Tier Two 2-hour kill test has been developed into a fully detailed protocol by AlControl Laboratories to make it accessible to all those looking for an appropriate test for hard surfaces in the absence of a published standard. See the Find Services page for labs familiar with this test protocol.

The protocol is provided in the downloads below along with the certificates of analaysis for 14 commonly available approved copper alloys. The test certificates include the alloy ISO designation, test results (including controls) and a statement confirming the test has been passed. The alloys are all those listed in Publication 214:  Antimicrobial Copper Alloys – Guidance on Selection.

Αναφορές

OECD Guidance Document on Quantitative Methods for Evaluating the Activity of Microbicides used on Hard Non-Porous Surfaces. ENV.JM.MONO(2014)18.

H T Michels, J O Noyce, and C W Keevil. Effects of Temperature and Humidity on the Efficacy of Methicillin-resistant Staphylococcus Aureus Challenged Antimicrobial Materials Containing Silver and Copper.  Letters in Applied Microbiology, 49 (2009) 191-19.

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