Age-old technologies jostle for position

 Health Estate Journal highlights the contrasting claims made by both “sides”, and reports on two recent studies in particular, one expounding the advantages of copper, and the other painting an equally positive picture for silver.  With silver ion and copper alloybased antibacterial materials’ proponents each vigorously promoting their respective technologies, a recent scientific study (Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper) by personnel including a top UK microbiologist compared the effectiveness of silver ion, copper alloy, and stainless steel surfaces in combating bacteria at what the researchers claimed were temperatures in the order of those typically encountered in hospitals. According to the UK-based Copper Development Association (CDA), the study vindicated the copper community’s claims that copper alloy-based surfaces and materials are “more effective” than those incorporating silver ions in combating bacteria in a “real-world hospital” environment. Carried out with support from the International Copper Association and the US-based Copper Development Association Inc, the study was undertaken by three individuals – Harold T Michels, senior vice-president of technology and technology services at the Copper Development Association Inc, Dr Jonathan Noyce, a post-doctoral research fellow in microbiology at the University of Southampton, and Professor C.W (Bill) Keevil, head of the microbiology group and director of the environmental healthcare unit at the same university. The testing was undertaken in the university’s own microbiology laboratories, and the results first appeared in a recent issue of Letters in Applied Microbiology. The CDA, which issued a press release shortly after the study’s publication highlighting the results, and in particular (from its standpoint) the silver technology’s apparent shortcomings in the testing, said the research was especially noteworthy as the first to test the anti-bacterial efficacy of silver ion-containing materials “at the lower temperature and humidity levels typical of indoor environments, such as those found in hospitals”, rather than at the high temperatures (of around 35°C) and high humidity (90% or higher relative humidity) typically used in previous tests. Angela Vessey, Copper Development Association director-general, said the CDA’s view was that many of the tests demonstrating silver’s anti-microbial effectiveness to date had been undertaken “purely in laboratory conditions and not under real-life hospital conditions, generally in a high humidity, high temperature environment”. In contrast this study, the CDA claims, saw the competing metals “tested at similar temperatures and humidities to those encountered in a typical hospital”.

Metal comparisons

Testing of the survival rates of MRSA on two types of silver-ion coated surfaces, five copper alloy surfaces, and a stainless steel surface, the CDA press statement said, showed “only minimal bacterial reduction” at 20°C and 22° humidity with the silver ion tested. Meanwhile the stainless steel, which served as the “experimental control”, showed “no measurable antimicrobial efficacy at any temperature or humidity level”. The CDA said the researchers had used copper alloys as a point of comparison because laboratory testing had shown that they are “effective in reducing over 99% of bacteria within two hours at room temperature (22°C) and normal humidity”. The authors concluded, following the tests, that “the high efficacy levels displayed by the copper alloys, at temperature and humidity levels typical of indoor environments, compared to the low efficacy of the silver ion-containing material under the same conditions, favours the use of copper alloys as antimicrobial materials in indoor environments such as hospitals”. Professor Bill Keevil, who led the research, elaborated: “Much of the testing undertaken so far to try to prove the anti-microbial efficacy of silver ion coatings has been done at relative humidity levels of 90% or even greater, and at temperatures of up to 35°C, as stipulated in the Japanese JIS Z 2801 standard, which was established back in 2000 to test the efficacy of silver incorporated into hydrophobic plastic surfaces.”