Healthcare-associated Infections
Table 1: Antimicrobial Copper Alloys are Effective Against These Pathogens
Acinetobacter baumannii Adenovirus
Aspergillus niger Candida albicans
Klebsiella pneumoniae Legionella pneumophila Listeria monocytogenes
Campylobacter jejuni
Methicillin-resistant Staphylococcus aureus (MRSA, including E-MRSA and methicillin-sensitive S. aureus [MSSA]) Poliovirus
Clostridium difficile (including spores) Pseudomonas aeruginosa Enterobacter aerogenes Escherichia coli O157:H7 Helicobacter pylori Influenza A (H1N1)
Salmonella enteritidis S. aureus
Tubercle bacillus
Vancomycin-resistant enterococcus (VRE)
Copper in Laboratory Studies
In 2000, the early laboratory studies from the University of Southampton indicated that copper cast alloys (e.g. brass and bronze) were able to reduce
E.Coli O157 cross-contamination during food-handling procedures. The research showed that although stainless steel may appear clean, bacteria can survive on these surfaces for considerable periods of time. In comparison, survival on many copper alloys is limited to just a few hours or even minutes. Due to the intrinsic characteristics of copper alloys, i.e. being homogenous and solid, wear resistant and durable, complete lifetime antimicrobial efficacy could be expected. These may then be utilised in facilities where bacterial contamination cannot be tolerated.7
One fundamental consideration in the early laboratory studies was which test of efficacy to employ. The only existing test for a solid material had been developed in Japan (JIS Z 2801) but stipulated conditions wholly different to a typical indoor environment, i.e. 35 ºC and in a relative humidity of 100 %. Copper alloys were shown to easily 'pass' this test, which required contact for 24 hours.
More appropriate standards were those based upon liquid disinfectants, like the current EN 1276, which used a more typical 20 ºC and allowed the inoculum to dry in sterile air. The Southampton team developed a modified version of this and was able to measure efficacy at specified times in order to obtain a kill rate curve. This test protocol has subsequently been verified in a number of other laboratories worldwide. The test is versatile and sensitive enough to allow comparison of different inoculum levels: from the disinfectant-based standard of 10 million colony-forming units (CFU) down to more typical hospital contamination levels such as 1,000 CFU or less. It has also been used to show efficacy at refrigeration temperatures. Comparative work using this test protocol (under typical indoor conditions) shows that silver-containing composites, like the stainless steel control, showed no efficacy.8
Subsequently, many papers have been published from numerous researchers expanding the understanding of the antimicrobial activity of copper alloys.9,10,11
As a simple comparison, against an antibiotic,
co-workers compared a copper alloy (CuZn37) with Aminoglycocide in a zone of inhibition test, showing comparable efficacy.12
In 2008, the US Environmental Protection Agency (EPA), following rigorous independent testing based upon the Southampton-developed
126 protocol, permitted the registration of nearly 300 copper alloys.13 This
allows public health claims to be made for the alloys under the terms of the registration, a first for solid materials.
Most recently, further developments of the laboratory test protocols have led to published work showing that efficacy on a dry surface can be as short as two minutes.14
The Southampton team also published
These have both been driven by attempts to make the laboratory tests similar to real life conditions.
work showing that even high inoculum levels of MRSA and VRE in droplet-like contamination events were eradicated in less than 10 minutes.15,16
Broad Spectrum Efficacy
In general, antimicrobial copper alloys are effective against bacteria, viruses, fungi and moulds, including these significant pathogens (see Table 1).
Mechanisms Work is ongoing on the mechanism14–16 by which copper exerts its
effect, but it is clear that the attack is a complex interaction rather than just one process interrupter. The speed at which the reactions occur complicates the research and a number of modes of action have been identified. Theories include membrane puncture and leakage, disturbance of osmotic balance and generation of free radicals causing oxidative stress. At some stage the cell DNA is completely destroyed, indicating that transfer of antimicrobial resistance should not be a factor of concern.
Clinical Trials
The first qualitative clinical trial was performed at Kitasato University Hospital in Japan in 2005.17
However, a fully quantitative trial was
initiated in 2007 on a 20-bed medical ward at Selly Oak Hospital in Birmingham, UK.
'Hot spot' touch surfaces were identified by a team of clinicians and microbiologists. The components included dressings trolleys, light switches, taps, door and equipment handles, push plates, grab rails and over-bed tables. These were upgraded to copper or copper alloy and placed on the ward over the course of six months. Once installed, the clinical assessment ran for three months and was able to report 90–100 % reductions in contamination on copper surfaces compared with controls. Standard cleaning procedures and products were used throughout the trial.18
Subsequently, a clinical trial in ICU rooms at Calama Hospital in Chile reported similar reductions. Notably, this region has regular daytime humidity levels of just 6 %.19
In a recent out-patient study, not only was the reduction in microbial burden confirmed but a 'halo' effect was observed: reduced contamination in the immediate vicinity of the copper surfaces. The copper surfaces were calculated to reduce the risk of exposure to environmental microbes by a factor of 17.20
Infection Rates
In a three-centre clinical trial (see Figure 1) completed in June 2011, the first proof of improved patient outcomes was reported. The trial initially carried out an observational assessment of key touch surfaces and contamination levels in an ICU environment, identifying which room components to upgrade to copper alloys.
EUROPEAN INFECTIOUS DISEASE
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