Bacteria killer: testing has proven that copper kills certain disease-causing bacteria. Now that the U.S. EPA recognizes that fact, copper parts could become hospitals' newest weapon against "superbug" MRSA.

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Several copper alloys are now recognized by the U.S. Environmental Protection Agency (EPA) as having the legal standing to claim the material kills certain bacteria that are a concern to public health, including the hospital "superbug."

Copper's antimicrobial benefits have been known intuitively for thousands of years. Egyptians used copper to sterilize drinking water and wounds, and the Aztecs treated sore throats with copper.

"Back in Greek and Roman times, people used copper for several health-related applications," said Jim Michel, manager of technical services for the Copper Development Association (CDA), New York, which spearheaded the campaign for copper's antimicrobial status. "They didn't know why, but they knew [copper] did something positive."

Now, after extensive testing and negotiations, lead by Harold Michels, senior vice president for CDA, and more than a year waiting for a decision from EPA, copper can legally be associated with public health claims that are backed by science. According to the EPA registration, certain copper alloys:

* continuously reduce bacterial contamination, achieving 99.9% reduction within two hours of exposure;

* kill greater than 99.9% of bacteria within two hours of exposure;

* deliver continuous and ongoing antibacterial action, remaining effective in killing greater than 99.9% of bacteria within two hours, even after repeated wear and re-contamination;

* help inhibit the growth of bacteria within two hours of exposure before and after cleaning and sanitizing.

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Copper's antimicrobial properties are a supplement to standard infection control practices. Together, they can reduce the number of disease-causing bacteria found in hosptial rooms.

Prove It

In order to legally make public health claims related to antimicrobial copper alloys, a material must be registered with EPA. Some products, such as commercially available silver-ion coatings, are registered under a treated article exemption, which means the product only protects the item containing the antimicrobial ingredient (for example, fungicide) and not the user. But in order to make a public health claim, EPA-approved efficacy tests are required.

Certain antimicrobial gases and liquids, such as sterilizers, disinfectants and sanitizers, are all products that have been legally registered to make a public health claim. However, EPA didn't have a template for CDA to follow when the organization first broached the possibility of registering copper as antimicrobial because the agency never before had given a solid surface material a public health registration under the Federal Insecticide, Fungicide and Rodenticide Act. The organization wanted to treat the prospect with caution.

"It was an unprecedented case," Michel said. "We had to go through every step and negotiate the protocols. Initially, we had to determine what kind of evidence the EPA would accept."

After several meetings, EPA approved three protocols. The required test results show that copper kills bacteria, that it stays effective at killing bacteria even after wet and dry abrasion (to prove that its antimicrobial property will not wear away), and that it continuously kills bacteria after repeated contamination.

The efficacy tests were conducted against five different kinds of bacteria in accord with EPA Good Laboratory Practices, which ensure that protocol were followed and facilitate EPA audits. The tests concluded that copper was effective in killing Methicillin-resistant Staphylococcus aureus (MRSA)--one of the most virulent strains of antibiotic-resistant bacteria and a common cause of hospital and community-acquired infections (Figs. 1-2). The other bacterium tested and approved were Escherichia coli O157:H7 (E coil), Pseudomonas aeruginosa, Staphylococcus aureus and Enterobacter aerogenes.

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Next Steps

Copper's antimicrobial properties should be particularly advantageous in applications where the surface is frequently touched key areas where disease-causing bacteria live. Initial prototype applications for copper components include IV poles and hospital hardware, such as door handles and chair arms.

The eventual applications are wide and varying, but it will require a change in what the health community perceives as clean and sanitary. Stainless steel is a popular material in hospitals for its clean look, and coatings are often used to achieve a bacteria fighting or neutralizing surface. But coatings wear off, and stainless steel showed no indications of antimicrobial properties in the tests conducted as part of copper's EPA application.

Copper's antimicrobial properties go beyond a surface coating, and provided the surface is clean, copper will continue to kill bacteria after wear and abrasion. To be effective, no other surface coating can be applied to copper parts to avoid tarnishing. Tarnished copper or bronze can look unsanitary, even when it isn't, and this could lead to a perception problem. However, testing has shown that tarnished surfaces maintain their antimicrobial efficacy.

EPA's registration, based on the results of the tests, includes 275 copper alloys, 48 of which are cast alloys. The cast alloys are included in Antimicrobial Copper Alloys Group II, along with a few wrought alloys (Table 1). CDA hopes to add another series of alloys, which would include more cast alloys, but before that happens, certain issues are being addressed to facilitate the widespread use of copper castings in public health applications.

During protocol discussions with EPA on alloys that could be included, the federal agency objected to the inclusion of any alloy that included less than 0.1% lead, chromium and arsenic. Cast copper alloys often contain higher percentages of these elements to improve their hardness and strength, which narrowed the range of cast copper alloys that could be considered in the registration. EPA also prefers all residual elements in the alloys to be less than 0.1%. Michel said CDA is working to adjust the UNS copper classification to include a series of alloys that has a maximum of 0.09% residual elements.

"If someone makes an alloy, they will probably get a call from me to see if they can get the residual elements down to 0.09% in order to include them," Michel said.

Broadening the range of alloys included in the EPA registration is one of three main priorities CDA has identified for the coming year. The other two are setting up a product stewardship program--as mandated by EPA--and setting up the registrations at the state level.

The stewardship program plan has been be submitted to EPA and is waiting for approval. The program will include a stewardship website and outreach to the infection control and associated healthcare community.

Currently, CDA alone holds the public health registration with the EPA. Additionally, it must register with every state. Then members of CDA can register their products with the EPA and by state using the same data submitted for CDA's initial registration.

"We're hoping the process of registration will take companies less than a year," Michel said. "Then we will have registered manufacturing companies able to make the legal claims about the products they produce."

For More Information

"Blocking Food's Bacteria," S. Wetzel, Engineered Casting Solutions, Sept./ Oct. 2007, p. 24.

Shannon Wetzel, Senior Editor

Table 1. Antimicrobial Copper Alloys Group II

UNS #       % Copper

C19810        94.8
C21000         95
C22000         90
C22600        87.5
C40500         95
C40860        94.8
C41000         92
C41120        90.5
C42000        89.5
C42200        87.5
C42220        89.5
C42500        88.5
C51000        94.8
C51080        94.5
C51900        94.8
C51900        93.8
C51980        93.5
C52100         92
C52180        91.8
C52400         90
C52480        89.6
C55180         95
C55181        92.8
C55280         91
C55281         89
C55282        88.3
C61000         92
C61300        90.3
C61400         91
C61500         90
C61550         92
C61800         89
C63800         95
C64200        91.2
C64210        91.6
C64730        94.6
C64780        94.5
C64785        88.1
C64790        94.3
C66200        88.8
C70400        92.4
C70500        93.2
C70600        88.6
C70610        87.3
C70620         88
C70690         90
C70700         90
C70800        88.5
C72500        88.2
C72650        87.5
C89320         89
C95200        87.7
C95210        87.8
C95300         89
C95600        90.3
C96200        88.6