EPA Regulatory Testing
The efficacy testing required by the EPA is briefly described and the test results are summarized below. For details, go to Michels and Anderson (2006).
The tests were conducted in accordance with EPA Good Laboratory Practices (GLP). Adherence to EPA GLP testing insures integrity and accuracy of the data required for registering products for public health use, and facilitates EPA audits of the test data. GLP tests were conducted at ambient temperature on two or three separately manufactured lots of five copper alloys, which range in copper content from 65% to 100%. Specifically, two to three lots of each alloy were mandated for the S. aureus and E. aerogenes, Methicillin-Resistant S. aureus (MRSA), P. aeruginosa and E. coli O157:H7 tests. Note that the inoculum, expressed as CFU/sq, is a measure of the number of viable bacteria* placed in the copper alloy surface. A description of the testing protocol and results has been published**. Vancomycin-resistant enterococcus (VRE) is not discussed in Michels and Anderson (2006) because the VRE tests were not conducted until after the article was published.
The three EPA-approved GLP test protocols are:
1. Efficacy as a Sanitizer: measures surviving bacteria on alloy surfaces after two hours
(median inoculum ~ 40 million CFU/sq. in.) Does it kill bacteria within the two hour test?*
2. Residual Self-Sanitizing Activity: measures surviving bacteria on alloy surfaces before and after six wet and dry wear cycles over 24 hours in a standard wear apparatus (median inoculum ~40 million CFU/sq. in.) Does the sanitizing capability wear off?
3. Continuous Reduction of Bacterial Contamination: measures surviving bacteria after eight repeated inoculation of the alloy surface in a 24-hour period without intermediate cleaning and wiping
(median inoculum ~10 million CFU/sq. in.) Will it keep working when repeatedly reinoculated?
The results of the 180 EPA GLP tests, involving three test protocols, six different alloys, and six different bacteria are shown in the table above and are summarized below.
In the Efficacy as a Sanitizer test, reductions in live bacteria of >99.9% are seen on copper alloys in all 84 tests. (Note that >99.9% equates to greater than 99.9% killing.)
In the Residual Self-Sanitizing test, reductions in live bacteria of >99.9% are seen on copper alloys in all 84 tests.
In the Continuous Reduction of Bacterial Contamination test, reductions in live bacteria of >99.9% are achieved in 73 out of 84 tests. Reductions ranging from 99.6% to 99.9% was achieved in 10 of 11 tests, while 1 test was recorded at 99.3% loss in viable CFU.
In summary, 241 out of 252 tests showed >99.9% reduction, while In the 11 other tests reached reductions of >99%.
These result are a strong testament to the ability of copper to kill bacteria*, especially when one considers that the number of bacteria placed on the copper was an average of at least 10 million CFU/sq. in. The amount of bacteria used in the EPA test, 10 million CFU/sq. in., is 10,000 times higher than he amount commonly found on non-copper surfaces in hospitals (<1,000/sq. in.***).
By any measure, the above test results confirm the the strong antimicrobial properties of copper against bacteria and is also seen in most experiments performed in the research laboratory setting.
** H. T. Michels and D. G. Anderson, Antimicrobial regulatory efficacy testing of solid copper alloy surfaces in the USA, pp. 185-190, Metal Ions in Biology and Medicine: Vol. 10, 2008, Editors: Ph. Collery, I. Maymard, T. Theophanides, L. Khassanova, T. Collery. John Libbey Eurotext, Paris ©, 2008
***M.G. Schmidt, et. al., Sustained Reduction in Microbial Burden on Common Hospital Surfaces through Introduction of Copper, JCM, 50: 2217-2223, 2012