Copper: An antimicrobial super-agent

Professor Bill Keevil is the Head of the Microbiology Group and Director of the Environmental Healthcare Unit at University of Southampton. His continued research includes the study of physiology and adaptive mechanisms for survival of pathogens and biofilms in the environment.

The benefits of copper to human health have been known since Antiquity, even though the Germ Theory of microbial infection was not developed until the 1800s. Ancient Egyptians recognised that copper could be used to sterilise drinking water and treat wounds, and Hippocrates in Ancient Greece and the Aztecs treated leg infections with various copper salts. As early as the 1850s, it also was recognised that copper workers in Paris were immune to the ravages of cholera during several devastating outbreaks.

Jumping ahead to the late 1970s and early 1980s, interest in the application of copper to help maintain water quality grew from the emergence of maladies such as Legionnaires’ disease and the recognition that the causative Legionella bacteria were spread from contaminated drinking water and cooling tower water supplies.  Investigations in controlled laboratory experiments showed that using copper could eliminate the habitat for, and retard the growth of, the pathogen by reducing formation of biofilm on plumbing tube surfaces. Similarly, in food studies, copper was proven to retard “burger bug” (E. coli O157) – the disease associated with the consumption of contaminated minced beef or of water contaminated by animal faeces – on copper and copper alloy plumbing surfaces. More recently, the same has been proven for other copper surfaces and pathogens that infect food supplies, including Salmonella enteritidis.

Today, we face a continual war in healthcare against “superbugs”, such as antibiotic-resistant Staphylococcous aurues (MRSA), which are responsible for many healthcare acquired infections.  A 2008 report from the European Centre for Disease Prevention and Control estimated that between 8-12% of patients suffer harm from the healthcare they receive, resulting in over 4 million infections per annum. Other studies, such as the 2006 UK National Audit Report, show that such infections can be reduced by one-third when certain infection prevention and control measures and structures are put in place. As a result of these and other rigorous studies, the European Commission recommend that Member States use such measures, and the U.S. Environmental Protection Agency in 2008 registered 275 alloys (with greater than 65% nominal copper content) as antimicrobial materials, allowing the manufacturers to legally make public health claims. The list now includes alloys with greater than 60% copper content, and hospital trials have been launched worldwide to investigate the antimicrobial claims for copper in a busy healthcare environment.

Carefully controlled trials, using copper in items such as door handles, push plates, taps, over-bed trays and toilet seats, have yielded encouraging preliminary results. A 90% reduction in microorganism contamination on touch surfaces have been reported in the USA, UK, Chile, South Africa and Japan. Other laboratory studies also showed that copper surfaces can kill influenza A strain H1N1. This is particularly important because influenza is transmitted by hand contact, and therefore it shows that good hand hygiene and surface cleaning could be more important than wearing a mask during an epidemic or pandemic.

So why does copper have these beneficial antimicrobial properties? Copper surfaces are antimicrobial because they release ions upon being touched by a microorganism, and these ions can interfere with the cellular membrane function, destroy the cellular membrane structure and inhibit cell respiration and population growth.  Dry copper surfaces are actually “self-sterilising” and therefore operate 24 hours a day, all year.

These are just some of the properties that show how copper can be used to help increase food, water and healthcare safety.  In this never-ending war against superbugs and harmful pathogens, we need every prevention barrier at our disposal to combat their continual evolution. The choice of which copper alloy to install in a particular environment depends on design requirements such as eventual use, aesthetics and metallurgical properties. It is important that we continue working to understand the benefits of copper contact surfaces for healthcare, public buildings, public and private transport and food processing establishments. Antimicrobial copper is key to a European future with reduced infection, morbidity, mortality and the associated healthcare costs.