A recent report published in the New England Journal of Medicine reminds us of the almost miraculous power of copper to kill microbes on contact. The study found no detectable amounts of the SARS-CoV-2 virus after four hours on a copper surface. Compare that to the virus lasting three days on plastic, two days on stainless steel and one day on cardboard.

While the confirmation of copper as a killer of the SARS-CoV-2 is new, we have known of copper’s lethality to germs for thousands of years—long before we knew of germs.

A History Lesson Forgotten

In the ancient armies of Egypt and Babylon, soldiers found that scraping their bronze (copper and tin) swords into wounds would reduce infection. In India, water was stored in copper pots to prevent illness.

In the 19th century, a physician noticed that none of the workers at a copper smelter in Paris were getting cholera, a bacterial disease. Waves of cholera were sweeping through Paris, killing thousands and filling city hospitals. Jewelers, goldsmiths, boiler makers—who also worked with copper and copper alloys—were also spared. In 1865, cholera killed 6,176 Parisians out of a total population of 1,677,000, a ratio of 0.37 percent. Of those who had contact with copper, only 45 had succumbed to the disease, a ratio of 0.05 percent.

The existence of disease-causing microbes, be they amoebas, bacteria or viruses, has been followed by findings of their inability to survive on copper. Even the hardiest of pathogens—the ones that fall into the frightening class of diseases referred to as HAI, or healthcare-associated infections—the super villains that run rampant in hospital environments and are impervious to every chemical, antibacterial medicine, or antiviral treatment, have their kryptonite. A 2013 study by Dr.Cassandra Salgado found that HAI rates in three intensive care units (ICUs) with copper clad surfaces were 58 percent lower than in standard ICUs.

How Copper Kills





Killing by contact. Shown is the tentative events in copper’s contact killing. A: Copper dissolves from the copper surface and causes cell damage. B: The cell membrane ruptures because of copper and other stress phenomena, leading to loss of membrane potential and cytoplasmic content. C: Copper ions induce the generation of reactive oxygen species, which cause further cell damage. D: Genomic and plasmid DNA becomes degraded. (Image courtesy of American Society of Microbiology.)

In trace amounts, copper is essential to most living organisms, where it functions in various chemicals to cross-link collagen, synthesize melanin, and defend against oxidative damage. On the other hand, the reduction-oxidation, or redox, properties of copper can also cause cell damage. A number or chemical mechanisms have been suggested here.

A little copper won’t kill you. Copper clad surfaces in an intensive care unit are shown circled. Copper cladding was found to reduce HAI, or healthcare-associated infections by 58 percent in one study. (Image courtesy of Medical University of South Carolina.)

TABLE 1.The Killing of Microbes on Copper Surfaces

Contact killing of microbes by copper surfaces Species Killing time* Salmonella enterica 4 h Campylobacter jejuni 8 h Escherichia coli O157 65-75 min MRSA 45 min EMRSA-1 60 min EMRSA-16 90 min Listeria monocytogenes 60 min Mycobacterium tuberculosis 5 to 15 days Candida albicans 60 min Klebsiella pneumoniae 60 min Pseudomonas aeruginosa 180 min Acinetobacter baumannii 180 min MRSA 180 min Influenza A virus (H1N1) 6 h C. difficile vegetative cells and spores 24-48 h C. difficile vegetative cells 30 min C. difficile dormant spores Unaffected in 3 h C. difficile germinating spores 3 h Pseudomonas aeruginosa 120 min Escherichia coli 1 min Acinetobacter johnsonii A few minutes Pantoea stewartii 1 min Pseudomonas oleovorans 1 min Staphylococcus warnerii A few minutes Brachybacterium conglomeratum A few minutes Aspergillus flavus 120 h Aspergillus fumigatus >120 h Aspergillus niger > 576 h Fusarium culmonium 24 h Fusarium oxysporum 24 h Fusarium solani 24 h Penicillium crysogenum 24 h Candida albicans 24 h Enterococcus hirae 90 min Different Enterococcus spp. 60 min Candida albicans 5 min Saccharomyces cerevisiae 30 s Source: Metallic Copper as an Antimicrobial Surface. *Or undetectable.

Spread by Surface Contact

COVID-19 is a disease that affects the respiratory system and is spread primarily by person-to-person contact. You can pick up the virus directly from a person coughing or sneezing on or near you. That is the most common way the disease is spread, according to the Centers for Disease Control and Prevention (CDC).

“It may [italics added] be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this is not thought to be the main way the virus,” says the CDC on its website at the time of this writing. It took until 1987 for the CDC to recognize the fomite (surface) spread of nosocomial (of hospital origin) infection, according to a Applied and Environmental Microbiology paper. By then research was erupting that confirmed a “multifactorial model of disease spread,” creating a growing body of evidence for the role of contaminated surfaces in the spread of viral infections. In fact, some viruses were only spread via contaminated surfaces. A 10-year study of the rhinovirus (common cold) in 343 adults found that the majority of infections were due to surface transmission. An aerosolized(direct) transmission was found to infect only 2 of 40 children, leading researchers to conclude that aerosol, or direct, transmission was a secondary to surface contamination or close contact as a spreader of HPIV1 (human parainfluenza virus type 1).

The popular scientific press, the general news media, governments, and the public do not appear to be waiting for the CDC to arrive at a conclusion on the role of surfaces in disease spread. Public warnings to wipe down surfaces abound, hand sanitizer flies off the shelf, and hand washing is at an all-time high.

So Why Isn’t Copper Everywhere?

You wonder, in the age of the coronavirus, why every hospital or restaurant surface isn’t covered with copper? From doorknobs, to toilets, to emergency rooms, to food preparation surfaces in every kitchen in hospitals, restaurants, and elsewhere.

A study of the effectiveness of brass door knobs in killing off any viruses left on them, while disparaging stainless steel—a relatively welcoming environment—was published in 2009 by the Copper Development Association. It was mostly ignored.

There are several reasons why hospitals may be slow to react.

As previously noted, the CDC has not definitively declared that COVID-19 can spread from contact with contaminated surfaces. For the institutions that need to justify how nothing needs to change—that stainless steel and plastics are still the materials of choice—the CDC has served a purpose.

Copper is not cheap. Copper pipes have to locked up on construction sites to prevent theft. Scrap metal suppliers will buy copper at $2.15 a pound, where as aluminum only commands $0.68 a pound. Phone wire (made of copper) strung in Africa kept mysteriously disappearing, a mystery that was solved only after copper jewelry was observed in abundance in local markets.

Copper is hard to maintain. Copper easily and quickly acquires a greenish patina of copper oxide. While that does not seem to lessen any of its microbial lethality, it makes facility managers want to scrub the surface back to a lustrous copper sheen. So, there are higher maintenance bills for copper. Stainless steel is (deceptively) clean-looking with no scrubbing or maintenance whatsoever.

If stainless steel became the shiny star of hospitals, it was plastics that crushed it as a material for hospital equipment. It was cheap. It could be molded to any shape in any color. It was everywhere. One study after another showed how plastic harbored contagion—most recently the COVID-19 virus—more than other material tested, but we looked the other way.

A lingering perception that copper is toxic may be holding the material back. While trace amounts of copper are vital to most organisms, as we have noted, large amounts can be poisonous. Copper sulfate is used as a fungicide and was found to be poisonous to humans at a gram dosage (11 mg/KG). But a little copper won’t hurt large organisms. Healthy humans can eliminate a little excess copper—except for those with Wilson’s disease, a recessive genetic disorder characterized by an inability to eliminate copper from the body resulting in toxic levels of copper in the liver and brain.

Some worry about copper cookware. Copper should not come in direct contact with acidic foods like tomatoes, which will cause a reaction and create copper compounds and ions, but most copper cookware is lined with another metal or a clear coating.

The official drink of the coronavirus? Moscow mule, served in a copper cup at Rye in San Francisoo. Copper has been proven to kill the SARS-CoV-2, the virus that causes COVID-19, just as it has been known to kill other microbes on contact. (Image courtesy of Wikipedia.)

References

Copper Destroys Viruses and Bacteria. Why Isn’t It Everywhere? Shayla Love, Vice.com March 18, 2020.

Metallic Copper as an Antimicrobial Surface, Gregor Grass, Christopher Rensing, and Marc Solioz, Applied and Environmental Microbiology, March 7, 2011.

Significance of Fomites in the Spread of Respiratory and Enteric Viral Disease, Stephanie A. Boone, Charles P. Gerba, Applied and Environmental Microbiology, March 13, 2007.