This morning, when walking in from my car to my office in the hospital, I had to open 6 doors and press 2 elevator buttons. With each door handle and elevator button, I was having contact with someone else’s fomites. Fomites are the small droplets that are formed when a person coughs or sneezes and are the primary way that respiratory viruses get transmitted. Bacteria, such as Staph aureus, are instead usually transmitted by skin contact with infected tissues, for example, by touching body secretions containing bacteria. In both situations, it is the hands that are the primary conveyance mechanism – whether they touch a person infected with Staph or whether a person with the flu blows their nose into a hand-held Kleenex. Anything that those hands touch can spread the viruses or bacteria in those fomites. Those door handles and elevator buttons that I touched this morning contain the fomites of hundreds of patients and hospital staff.
Certain materials are inherently more antimicrobial than others. Most hospital door handles are made of stainless steel or aluminum because steel and aluminum wipes off easily and because it’s shiny appearance looks clean. However, it turns out that steel and aluminum do not have antimicrobial properties so viruses and bacteria can survive on steel knobs, buttons, and handles for hours. Copper, on the other hand, has potent natural antimicrobial properties. This has been known for centuries – for example, copper water vessels were preferentially used in ancient times because water would be of better quality when transported in copper containers as opposed to containers made of other materials.
The medical literature about copper’s antimicrobial properties is extensive and it has been shown to inhibit/inactivate fungi (such as Aspergillus and Candida), viruses (such as influenza and polio), and bacteria (such as E coli, Clostridium difficile, and MRSA).
One of the problems with copper as a building material is that it tarnishes and then looks old and dirty. However, copper can be combined with other metals to form alloys such as brass (copper + zinc) and bronze (copper + tin) which are more commonly used for building fixtures. Although these alloys are better than steel with respect to their antimicrobial properties, then are not quite as effective as pure copper. For example, 99.9% of E. coli are killed within 120 minutes on copper surfaces but similar kill rates take up to 270 minutes on brass surfaces and 270 minutes on bronze surfaces. In contrast, E. coli can survive on stainless steel surfaces for weeks. The antimicrobial properties of copper are temperature dependent. At temperatures of 4 degrees C (40 degrees F), bacterial killing requires 1 hour longer than at 20 degrees C (70 degrees F).
As we renovate our hospitals in the future, we should look back to using copper and brass door handles, cabinetry fixtures, and buttons. Copper may not look as clean and sterile as stainless steel but looks can be deceiving. A $4 door handle may just have as big of an epidemiologic impact as a $20,000 ultraviolet room sterilizer…
March 10, 2020