Online Exclusive: Antimicrobial copper alloys defend against infectious pathogens

Copper alloys offer many properties that can make them ideal for high-speed machining, including excellent surface finishes, superb chip control and long tool life, as well as environmental benefits including high scrap value and recyclability. But beyond ideal manufacturing properties and profitable machinability, brass and other copper alloys also provide self-sanitizing protection against surface pathogens, which makes them a valuable defense against pandemic infections.

The built environment includes many objects and surfaces that harbor high amounts of potentially deadly bacteria and viruses, and crafting these high-touch items from brass or other copper-based alloys dramatically curtails their infectious potential. Pathogens can persist on plastic or stainless steel for days, months and even years, enabling them to spread by touch throughout public and private facilities (Kramer, Schwebke, and Kampf, 2006). Because of the large numbers of people who visit and work in public spaces, viruses spread especially rapidly through them, able to move from a single doorknob and tabletop in an office building to between 40% and 60% of its visitors, employees and high-touch surfaces within two to four hours (Reynolds et al., 2016).

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To counter this infectious potential, copper alloys such as brass offer proven antimicrobial properties. Alloys with a minimum of 60% copper content continuously kill bacteria, viruses, fungi, and other human pathogens on their uncoated surfaces (Grass, Rensing, and Solioz, 2011). These self-disinfecting properties apply to the virus that causes COVID-19, as well as to other microbes that cause infections resistant to treatment with antibiotics.

Copper alloys kill pathogens through multiple biological mechanisms. First, pathogens identify copper ions as a nutrient that is essential for basic cell functions in small amounts. Once inside a pathogenic cell, copper ions can impede normal functions, including respiration and metabolism, and compromise the integrity of the cell membrane. In some cases, copper ions destroy the DNA of the pathogen itself (Copper Development Association, 2020, p. 81).

Depending on alloy composition, age and oxidation can develop a patina on copper-alloy surfaces, which continue to display the same, if not even better, virus-killing properties as unoxidized alloy surfaces (Grass, Rensing, and Solioz, 2011). Best of all, the antimicrobial properties of copper alloys are inherent to the material itself and do not rely on human behavior for their effectiveness.

Despite the well-documented self-disinfecting capabilities of copper alloys, facilities typically rely on manually applied chemical cleaners and disinfectants instead. Hand washing and surface cleaning offer only short-term, limited protection because they rely on human beings to perform specific actions – and to do so correctly. Even after cleaning, pathogens can remain on many common surfaces in hospital settings, and for full antimicrobial effectiveness, many disinfectant chemicals must have time to dry, which can be impractical.

Especially in public-health environments, reduction of surface-borne pathogens requires continuous intervention without human action. A one-time investment in self-sanitizing uncoated copper alloys for high-touch surfaces provides continuous protection between cleanings as a highly effective supplement to standard practices of infection control, which enhances efforts during a pandemic.

As a recent U.S. government-funded study conducted by researchers at the National Institutes of Health and the Centers for Disease Control and Prevention reported, on uncoated copper-alloy surfaces, the SARS-CoV-2 virus, which causes the disease COVID-19, became inactive within four hours, compared to 24 hours on paper or cardboard, two days on steel or stainless steel, and three days on plastic (van Doremalen et al., 2020). Additional evidence comes from more than 250 scientific papers and research studies that support copper alloys' antimicrobial properties against a wide range of pathogens, including antibiotic-resistant superbugs such as MRSA, VRE and C. diff.

Scientific proof must underlie all claims of antimicrobial properties. The U.S. Environmental Protection Agency (EPA) regulates these claims, and requires researched evidence, along with proof that products do not harm people or the environment. In 2008, the EPA approved public health claims for the antimicrobial properties of copper alloys following extensive testing. That research showed that copper, brass and bronze continuously kill more than 99.9% of six deadly bacteria after eight exposures during a 24-hour period, with no cleaning between exposures. The EPA's registration applies to more than 500 unique copper alloys, including brasses, and makes these alloys the first solid-surface materials to receive EPA registration for public health claims of long-term, residual, continuous antimicrobial properties. (US EPA, n.d.).

The use of antimicrobial copper alloys can prevent or at least minimize the staggering costs of hospital-acquired infections (HAIs). Every year, 2 million HAIs cause more than 100,000 deaths and over $45 billion in unnecessary healthcare expenditures (Scott, 2009). Abundant research supports the use of copper alloys to minimize the enormous numbers of infectious agents on high-touch surfaces in health-care settings.

A multi-hospital clinical trial funded by the U.S. Department of Defense demonstrated that patients treated in hospital rooms with copper alloy touch surfaces experienced 58% fewer HAIs (Salgado et al., 2013). These results required conversion of less than 10% of the surface area of hospital rooms (Salgado et al., 2013).

Numerous hospitals around the world have deployed antimicrobial copper and brass materials for high-touch surfaces such as faucet and cabinet handles, door hardware, switch plates, railings, toilet levers, bed rails, patient call buttons and more. These conversions can pay for themselves in short order. Based on U.S. clinical trials, conversion of eight intensive-care rooms pays back its cost in 29.2 days because of the number of HAIs prevented and the moneys no longer spent on treating them (Copper Development Association, 2020, p. 54).

Copper alloys provide lasting antimicrobial benefits over decades of use. A study conducted with the New York City Transit Office of Strategic Innovation & Technology assessed the lasting antimicrobial properties of copper-alloy surfaces installed in Grand Central Terminal, constructed between 1903 and 1913. Brass rails, doors and shelves showed total bacterial loading well under the threshold considered to present risk to human health, whereas comparable steel and marble surfaces harbored pathogen levels nearly eight times the risk level (Copper Development Association, 2020, p. 55-58).

Conclusion
Handwashing and surface disinfection offer important interventions, but these intermittent events rely on fallible human behavior and do not provide continuous protection. By contrast, antimicrobial copper alloys work around the clock to kill bacteria and viruses continuously on frequently touched surfaces. Manufacturers can position the dramatic, lasting effect of these beneficial properties to increase the market reach of their products.

Additionally, manufacturing facilities can deploy antimicrobial copper materials on high-touch surfaces to provide an additional strategic line of defense against infection for their employees and customers. From water taps and flush handles in restrooms to showroom tables, work areas and breakrooms, manufacturers can make simple material substitutions that protect against transmissible disease. This easily implemented step conveys lasting continuous protection without further investment, and demonstrates industry commitment to employee well being as well as to public health.

References

Copper Development Association. (2020, August 21). Antimicrobial copper alloys: Self sanitizing surfaces to control the spread of human pathogens [PowerPoint slides].

Grass, G., Rensing, C., and Solioz, M. (2011). Metallic copper as an antimicrobial surface. Applied and Environmental Microbiology, 77(5), 1541-1547. doi: 10.1128/AEM.02766-10

Kramer, A., Schwebke, I., and Kampf, G. (2006). How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infectious Diseases, 6, 130. https://doi.org/10.1186/1471-2334-6-130

Morrison, J. (2020, April 14). Copper’s virus-killing powers were known even to the ancients. Smithsonian Magazine. Retrieved from https://www.smithsonianmag.com/science-nature/copper-virus-kill-180974655/

Reynolds, K. A., Beamer, P. I., Plotkin, K. R., Sifuentes, L. Y., Koenig, D. W., and Gerba, C. P. (2016). The healthy workplace project: Reduced viral exposure in an office setting. Archives of Environmental & Occupational health, 71(3), 157–162. https://doi.org/10.1080/19338244.2015.1058234

Salgado, C., Sepkowitz, K., John, J., Cantey, J., Attaway, H., Freeman, K., . . . Schmidt, M. (2013). Copper surfaces reduce the rate of healthcare-acquired infections in the intensive care unit. Infection Control and Hospital Epidemiology, 34(5), 479-486. doi:10.1086/670207

Scott, R. D. (2009). The direct medical costs of healthcare-associated infections in U.S. hospitals and the benefits of prevention. Division of Healthcare Quality Promotion, National Center for Preparedness, Detection, and Control of Infectious Diseases, Coordinating Center for Infectious Diseases, Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/hai/pdfs/hai/scott_costpaper.pdf

van Doremalen, N., Bushmaker, T., Morris, D. H., Holbrook, M. G., Gamble, A., Williamson, B. N., . . . Munster, V. J. (2020). Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. The New England Journal of Medicine, 382(16), 1564–1567. https://doi.org/10.1056/NEJMc2004973

United States Environmental Protection Agency. (n.d.) Updated Draft Protocol for the Evaluation of Bactericidal Activity of Hard, Non-porous Copper Containing Surface Products. Retrieved from https://www.epa.gov/pesticide-registration/updated-draft-protocol-evaluation-bactericidal-activity-hard-non-porous