Copper’s hygienic properties are well known but its antimicrobial properties continue to be quantified in the lab and in the field. The Copper Alliance highlights recent study results and testing developments
The latest research to emerge from the University of Southampton – where researchers are investigating the inherent antimicrobial properties of copper – shows the metal and many of its alloys will rapidly destroy norovirus, the highly infectious ‘sickness bug’. A presentation at the American Society for Microbiology’s 2013 General Meeting earlier this year stated that norovirus could not survive contact with copper and its alloys. The contamination model used was designed to simulate fingertip-touch contamination of a surface, and the researchers suggest that the use of antimicrobial copper surfaces in high-risk, closed environments (e.g. care facilities or cruise ships) could help reduce the spread of this communicable and costly pathogen.
The significance of this – and previous work demonstrating copper’s rapid efficacy against a wide range of bacteria, viruses and fungi – is that, given an estimated 80% of infections are spread by touch, frequently touched surfaces can act as reservoirs of infection, harbouring pathogens that can survive for days or even months, waiting to be transferred to the next hand that touches them. Those same surfaces – door handles, taps, light switches, hand rails and more – can be made from copper, or an antimicrobially effective copper alloy, and will actively destroy pathogens, continuously reducing bioburden.
While pure copper offers the most rapid effect against pathogens in contact with it, many of its alloys – including the familiar brasses and bronzes – are also very effective, and they offer a range of enhanced properties such as strength, wear resistance and corrosion resistance. Collectively termed ‘antimicrobial copper’, these metals are available in colours ranging from oranges, reds and pinks, through the gold of brasses and warm brown of bronzes, right up to silver-coloured copper-nickels that have the appearance of stainless steel. This means the aesthetic of a particular installation can be considered, with colour-matching suites of products available.
Another advantage of copper alloys is that they are easy to manufacture, versatile, and hard-wearing. Unlike a coating, the materials are antimicrobial through and through, so even if they are scratched or dented, their efficacy is not impaired. Additionally, all antimicrobial copper items are fully-recyclable, contributing to sustainable design.
Antimicrobial copper touch surfaces are already being used in healthcare facilities around the world to augment existing hygiene procedures. Alongside regular hand-washing and surface cleaning, a clinical trial in the UK was the first to demonstrate that these surfaces continuously reduce bioburden by 90–100%.
Recently published data from a multi-centre US trial is the first to link this reduction in bioburden with an improvement in patient outcomes. The six most frequently touched near-patient surfaces in an ICU (bed rails, overbed tables, chairs, call buttons, data input devices and IV drip poles) were replaced with antimicrobial copper equivalents. The result was an 83% reduction in bioburden and a 58% drop in the patient’s risk of acquiring a healthcare-associated infection, compared with controls.
Professor Bill Keevil (left) and research fellow Sarah Warnes testing copper at Southampton University
Another significant finding is that more than 80% of infections were associated with environmental bioburdens greater than 5cfu/cm2, supporting the call for an environmental hygiene standard for hospitals. The trial reported that during patient care, antimicrobial copper surfaces generally held bacterial burdens at or below the threshold recommended immediately after a terminal clean (conducted when a patient vacates a room).
The deployment of copper is not a substitute for standard hygiene practices, rather an adjunct to them. Regular cleaning of antimicrobial copper items remains important, as heavy soiling may prevent pathogens from coming into contact with the active surface. Standard cleaning products and protocols have been used in clinical trials and installations around the world. Currently, the Copper Alliance – a global network of non-profit organisations that promote and offer technical assistance with the correct use of copper – is working with leading companies to progress the development of cleaning and disinfection products that act synergistically with copper to maximise efficacy and so help to maintain a more hygienic environment.
Testing of surfaces purporting to be antimicrobial has come under scrutiny in recent years, with the consensus now suggesting currently-published standards have limitations as they are not always representative of in-use conditions. While antimicrobial copper surfaces work whether contamination is applied dry or wet and at a wide range of temperatures, other materials require high temperature and humidity to be effective. As the ISO 22196 test is conducted at 35°C and 95% relative humidity, it clearly does not represent a normal clinical environment, and this is a concern as it casts doubt on marketing claims based upon this test.
Hand washing with a copper tap at Selly Oak Hospital, Birmingham, UK
To address this issue, the Copper Alliance is represented on the relevant panels of the British Standards Institution and ASTM International in the US to progress the development of more appropriate standards for testing antimicrobial hard surfaces. Test methods are currently being considered for both healthcare and the food industry.
The US Environmental Protection Agency approved tests are conducted at room temperature and humidity, and were used to assess antimicrobial copper. Subsequently it was the first solid material permitted to make public health claims in the US, and the tests formed the basis of a stewardship scheme established by the Copper Alliance to help manufacturers choose effective antimicrobial copper materials and specifiers identify efficacious products. Items approved under the scheme may display the Cu+ mark and use the Antimicrobial Copper brand. These signify that the product is a certified antimicrobial copper alloy – based on the EPA Registration – and the company is familiar with the technical requirements for producing an efficacious product (including not lacquering or coating the surface in a way that might interfere with its antimicrobial activity).
A common misconception about antimicrobial copper products is that they will be expensive. Material cost makes up only a very small percentage of a product’s overall price, and copper alloys are cost-effective materials to work with and form components from. The process scrap generated is sold back to the material suppliers for recycling and so helps offset manufacturing costs. Any marginal cost premium compared with standard components will depend on multiple factors including alloy choice, fabrication technique and volume of the production run.
An interesting economic assessment was recently undertaken by York Health Economics Consortium, part of the University of York, to evaluate the cost-effectiveness of installing copper touch surfaces in ICUs. Using the US clinical trial data as a basis, the consortium then applied UK infection rates and cost of infections in a worked example.
The work – presented at the WHO’s International Conference on Prevention and Infection Control in Geneva in June – culminated in a model1 predicting that the cost of replacing six key, frequently touched surfaces in a 20-bed UK ICU with antimicrobial copper equivalents (as in the US trial) will be recouped in less than two months, based on fewer infections and the resulting shorter lengths of stay.
Hard-wearing and available in a range of colours, antimicrobial copper surfaces will not wear away or lose their effectiveness, unlike coatings. With a US multi-centre trial showing just six antimicrobial copper surfaces can cut a patient’s risk of contracting an HCAI in half, and an economics assessment demonstrating rapid payback for hospitals, antimicrobial copper clearly offers the potential for a very attractive engineering approach to contamination control.
1. The model can be downloaded as an XLS spreadsheet from www.antimicrobialcopper.org