Unlocking copper’s astonishing antimicrobial efficacy

The Cu-Shield digital lock range was developed with assistance from Andrew Cross of ACT Surfaces Ltd, a consultant in the niche subject of antimicrobial materials. Andrew comments on how the 2020 Coronavirus outbreak has made everyone focus on items they touch and how infection spreads. Especially now as the combination of COVID-19 and winter pressures is an alarming double-blow for healthcare and for the economy, calling for additional preventative measures.

Research published in March 2020 in New England Journal of Medicine, [1] prompted the question: “Why does SARS-CoV-2 remain viable for such a short time on copper (only up to 4 hours) yet far longer (up to 72 hours) on plastic and stainless steel?“

Previous research [2] reported that Coronavirus (229E) remained viable for under an hour on copper, but for “several days” on other surfaces.

Whenever comparing antimicrobial materials, it is crucial to look beyond the headlines and examine the test methods and test protocols behind efficacy claims.

•  ISO 22196 is a commonly-used “proof of concept” test with a long test time (up to 24 hours) under “warm and wet” conditions, with samples covered with plastic film to prevent drying-out.
• When tested under dry (typical indoor) conditions, some widely-used antimicrobial materials had negligible effect whereas copper worked faster, with multiple mechanisms. [3]
• The test protocols behind the US EPA registration of copper had a maximum 2 hour exposure to copper, with a 50 microlitre droplet to simulate a splash contamination. [4]
• More recent tests show copper is effective within minutes against diverse pathogens, even antibiotic-resistant bacteria. [5]

Work is ongoing by OECD [6] and ISO to standardise test protocols. The ISO stated: “Biocidal surfaces are a valuable tool because they destroy or inactivate unwanted pathogens, thus contributing to a cleaner environment. However, the performance of such surfaces can vary, giving rise to the need for effective guidelines and test methods to ensure they are up to scratch.” [7]

The ISO recently created an expert committee ISO/TC 330 [8] to develop internationally-agreed test methods and guidance for assessment of any surfaces with antimicrobial activities, also their compatibility with different disinfectants and cleaning agents.

At ACT Surfaces Ltd, we welcome these developments and look forward to much-needed clarity enabling accurate comparison of antimicrobial materials: the robust body of evidence for copper [9] means you can be confident it actually works in real life.

SOURCES:

[1] van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med 2020;382:1564-7.

doi: 10.1056/NEJMc2004973

[2] Warnes SL, Little ZR, Keevil CW. Human Coronavirus 229E Remains Infectious on Common Touch Surface Materials. mBio. 2015;6(6):e01697-15. Published 2015 Nov 10. doi:10.1128/mBio.01697-15

[3] Michels HT, Noyce JO, Keevil CW. Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper. Lett Appl Microbiol. 2009 Aug;49(2):191-5. doi: 10.1111/j.1472-765X.2009.02637 .x. Epub 2009 Apr 25. PMID: 19413757; PMCID: PMC2779462.

[4] https://www.copperalloystewardship.com/clarifying-statements

[5] Dauvergne, E.; Lacquemant, C.; Adjidé, C.; Mullié, C. Validation of a Worst-Case Scenario Method Adapted to the Healthcare Environment for Testing the Antibacterial Effect of Brass Surfaces and Implementation on Hospital Antibiotic-Resistant Strains. Antibiotics 2020, 9, 245. https://doi.org/10.3390/antibiotics9050245

[6] http://www.oecd.org/env/ehs/pesticides-biocides/efficacytesting.htm

[7] https://www.iso.org/news/ref2570.html

[8] https://www.iso.org/committee/8017922.html

[9] Introductory overview: Michels HT, Keevil CW, Salgado CD, Schmidt MG. From Laboratory Research to a Clinical Trial: Copper Alloy Surfaces Kill Bacteria and Reduce Hospital-Acquired Infections. HERD. 2015 Fall;9(1):64-79. doi: 10.1177/1937586715592650. Epub 2015 Jul 10. PMID: 26163568; PMCID: PMC4561453.