Blocked Transmission

Words by
Tom Ough


It was March 2003, and an unfortunate 33-year-old, known only as patient YY, was suffering from intense diarrhea. The man was in Hong Kong for kidney treatment. While in the city, he visited his brother in Block E of Amoy Gardens, a vast housing estate that looks rather like a set of vertical shortbread cookies.


But try not to think of food as you consider what happened next. The stricken kidney patient had, at some point during the previous days, become infected with SARS (Severe Acute Respiratory Syndrome), a highly contagious illness that is caused by a coronavirus and is viewed as a serious pandemic risk. Patient YY was now disgorging colossal amounts of viral particles into the plumbing of Block E.

The plumbing at Amoy Gardens was poorly designed. Block E’s bathrooms had floor drains that were connected to the same outbound sewage pipes as the lavatories. In this method of plumbing, a water-filled S-bend prevents insects from entering and foul smells from escaping. These pipes are typically cleared by water draining from wet bathroom floors. However, because the residents happened to clean their bathrooms by mopping their floors rather than by splashing them with water, many of those S-bends were dry.

Unimpeded by a water barrier, the SARS particles were drawn up into each bathroom by their exhaust fans, where they descended onto residents’ possessions: taps, toothbrushes, toiletries, bath mats. Patient YY’s neighbors quickly started to become infected, passing on the virus in turn. More than 329 residents of Amoy Gardens came down with SARS, 42 of whom died.

Puzzled, epidemiologists sought to understand the source of the outbreak. Several theories were put forward, including animal vectors, such as rats, which spread microbial particles while scuttling across roofs. While the consensus that emerged among experts was that the virus spread primarily via airborne transmission, it also made use of another route: fomite transmission.1

Fomites, whose name comes from the Latin fomes, literally meaning ‘touchwood’ or ‘tinder,’ are inanimate surfaces or objects that carry infection. Amoy Gardens’ elevator buttons, door handles, and bathroom items were covered with imperceptible pathogens that passed from those objects onto people’s hands, which then found their way into their bodies via their mouths and noses.

Fomite transmission obeys a power law. Most square centimeters of our built environments transmit next to no disease (think of walls, which we rarely so much as brush in passing), but some are touched with extraordinary frequency.

These high-touch surfaces include the door knobs and door handles in Amoy Gardens and other busy buildings, as well as all manner of items found in settings from homes to hospitals: light switches, communal IT equipment, tables, bed frames, surgical accouterments. All these objects harbor pathogens—not just viruses, but also bacteria and fungi—which our tactile species then industriously and unwittingly spreads around. Fomites can also be aerosolized, traveling through the air on currents or breezes.

Amoy Gardens, a housing estate in Hong Kong, is home to more than ten thousand residents. Credit: Prosperity Horizons

What happened at Amoy Gardens was a localized incident, but it’s easy to imagine more outbreaks in which fomite transmission plays an important role. While it’s difficult to quantify precisely how much disease is passed along via fomites, we know fomite transmission often contributes to the severity of disease outbreaks and acts as a secondary pathway by which pathogens are spread.

Diarrheal diseases—attributed to viruses, such as noroviruses, which are spread via fomite transmission—killed about 1.5 million people in 2019. In 2010, seven members of a soccer team in Oregon were infected with norovirus after touching a reusable grocery bag, which was covered in viral particles, and then eating the food inside. A thorough disease-prevention strategy ought to address fomite transmission along with airborne transmission. Or, as a public health professor at the University of Hong Kong put it, "Intervening against multiple modes of transmission should be more effective than acting on a single mode."

While working for a biosecurity non-profit last year, I searched for neglected ways to make the built environment—our homes, shared buildings, towns, and cities—less prone to fomite transmission. Elementary solutions, such as handwashing, have been shown to reduce respiratory illnesses, like colds, in the general population by 21%, reduce the number of people who get sick with diarrhea by 29%, and reduce diarrheal illness in people with weakened immune systems by 58%. However, we cannot rely on people’s ability to wash their hands.2

This is why a simple and cheap alternative would be to make more surfaces that kill microbes, including viruses, on contact. When I say surface, I mean either the material from which an object is made or a spray that can coat such an object, i.e. “surface coatings”. After talking to experts and industry entrepreneurs, I became convinced that surface coatings rival the efficacy of traditional biocidal materials while being cheaper and non-toxic.


There is already excitement within the biosecurity community about another method of limiting fomite transmission: the use of ultraviolet light, which works by blasting bacteria and viruses with energetic photons that destroy their genetic material.

Although standard UV light damages human tissue, a shorter-wavelength variety, known as far-UVC, damages microbes without penetrating beyond the thin layer of dead skin cells that clings to the human epidermis. Scientists at several universities are investigating the efficacy, safety, and environmental toll of far-UVC light. One study that investigated the use of far-UVC against human coronaviruses found that shining three millijoules of energy per square centimeter of surface deactivated about 90 percent of viruses after eight minutes, and 99.9 percent of viruses after 25 minutes.

Far-UVC light could become a crucial tool against both aerosols and fomites, but it has weaknesses. At wavelengths below 240 nanometers, it produces ozone gas (O3), which can damage the lungs when inhaled. Ozone gas can be dealt with by air purification, but it is expensive to install and maintain new lighting systems; far-UVC lamps start at $500. An additional limitation is that a far-UVC lamp has to be in “sight of” a surface in order to kill microbes on it. Unless we install recessed floor lights in every hospital ward, and keep them on 24/7, far-UVC lamps will remain an exciting addition to our pathogen-fighting arsenal but not a cure-all.

We already have a widely-used method of sanitizing surfaces, of course, in a variety of bleach-based products. But bleach is a solution only in the sense that it is a solute with an active ingredient. Bleach belongs to a family of disinfectants that often contain sodium hypochlorite, a chemical that, when applied to any of a wide range of substances, causes oxidation: the loss of electrons. At a cellular level, oxidation is brutal. It renders proteins non-functional, inactivates key enzymes, damages DNA, and causes cells and viruses to break apart. Bleach is used worldwide in hospitals, on public transport, and in homes. It is cheap and easy to use, but it is also a blunt tool with its own drawbacks.

The overuse of bleach, as with most biocides, contributes to antibiotic resistance. This is because oxidation, brutal though it is, can be partially resisted. When the concentration of bleach is low, or when bacteria are regularly exposed to sodium hypochlorite, the cells upregulate the expression of efflux pumps to expel toxic substances. These toxic substances, from the perspective of a bacterium, include antibiotics.

Additionally, bleach and its fumes are toxic—you, too, are made of substances that can be brutalized by oxidation—and are associated with conditions such as asthma. It also needs to be reapplied at frequent intervals. Using bleach to kill the odd cold virus is like using acid rain to put out a fire.

Nevertheless, bleach has the power of the incumbent. Fail to disinfect your hospital and you will have lawsuits thudding onto your desk by the time you’re back from your lunch break. These circumstances mean that there is less demand for alternatives than there should be. Yet some of us are asking: Can we do better?

History gives us an alternative of sorts. If you happened to have a drink with some wealthy ancient Egyptians, they might well have served it in a copper vessel. Copper is a transition metal, the kind which has the propensity to lose electrons. This happens to copper when it is exposed to air and moisture. When copper atoms lose electrons, they become ions, and the positive charge of copper ions allows them to chemically interact with atoms they come into contact with. As with the comparable phenomenon of oxidation, this causes huge physical disruption to microbes: a wind of chaos that denatures proteins, degrades genetic material, and breaks viral envelopes and cell membranes.

A company called LuminOre will soon bring copper-coated air ducts to the market. Credit: Alfred Mitchell, courtesy of Tom Ough.

The Egyptians wouldn’t have understood the chemistry, but they knew that copper reduced the chance of illness. In hieroglyphs, the ankh symbol refers to both copper and eternal life. The metal was used for its antimicrobial properties by the Phoenicians, ancient Chinese, Greeks, Romans, Aztecs, and others. In the 18th century, copper was used to prevent the build-up of algae and other biological matter on ships’ hulls. Copper, and its alloys, are still used as antimicrobial agents in the modern world, and renewed medical interest in copper has led to reams of supportive research.

One study showed a 94% reduction in microbial burden on copper-coated beds, in a hospital’s intensive care unit, compared to control beds. Another study found that copper-alloyed surfaces reduce the rate of healthcare-acquired infections in an intensive care unit by 58%. Although some microbes can develop a certain level of tolerance to copper, just as they can with bleach, copper is much less toxic to humans and gives off no fumes.

Silver is another transition metal and, as such, is antimicrobial, but only to an extent. Those truly interested in this topic can refer to some additional research that I conducted as a younger man, when journalistic misadventure forced me into wearing the same “self-cleaning” pair of underpants for seven days. If you’d prefer to avoid the gnarly details, know that silver’s antimicrobial effect is enhanced by humid environments, but that, in this case, it stopped some way short of perfection.

Another drawback of silver, compared to copper, is that it is almost 100 times more expensive. This is why it is copper, rather than silver, from which we have traditionally made pennies. Zinc also has antibacterial effects, but its ions are less reactive and therefore less damaging to cells. Titanium oxide is another also-ran because it is photocatalytic, which means that it requires light to catalyze the reaction that kills microbes. Overall, copper is the strongest of these materials at killing bacteria. In nine hours, copper reduces the number of microbes on a surface by a factor of 100 million, according to one study, far outranking any metal aside from cadmium, which is toxic.

Other materials, such as the wings of cicadas, are antimicrobial by dint of their architecture. And these natural patterns can be replicated at the nanoscale. A company called Sharklet uses micron-level manufacturing to create plastic whose microscopic diamond pattern, like that of sharkskin, inhibits the multiplying of bacteria. But viruses are much smaller than bacteria and are viewed by experts as more of a challenge.  

Tiny, artificially-made structures (e.g. “nanopillars”) also provide a mechanical means by which to vanquish microbes, including viruses, by damaging viral particles with their sharp tips or disrupting their membranes with electrostatic charge. But nanotechnology-derived coatings are not likely to be widely sold anytime soon. “It would take a lot of Nobel Prizes to get vertically-aligned carbon nanotubes widely adopted and available in a tin of paint,” says Anthony Schiavo, senior director at Lux Research. Graphene-based materials are similarly enticing, but also prohibitively expensive. The cheapest carbon nanomaterials cost thousands of dollars per square meter. That price might make sense for surgical implants, but not for broad use.

As an all-rounder, then, copper is the best of the materials. Still, the wholesale replacement of existing surfaces would be pricey, encompassing both the cost of the metal itself and the labor required to install it.

Let’s imagine replacing, with a copper alternative, every light switch in American public-sector buildings: schools, hospitals, prisons, government buildings, and so on. Given that there are about 140,000 schools in the United States, we can safely assume that the total number of American public sector buildings is greater than 500,000. Multiply that by the 100-odd light switches that you’d expect per building, at a cost of roughly $20 each, judging by existing prices, and assume that the labor costs are a conservative $25 per switch. That’s a billion dollars on parts, plus $1.25 billion on labor—and that’s only for light switches.

Fortunately, there is a more practical option that makes use of the best of the metals we examined earlier. Rather than replacing all those high-touch surfaces, we should consider sprays with which to coat those surfaces in only a thin copper layer—an option much cheaper than wholesale surface replacement. Cold-sprayed copper kills more than 99.999% of bacteria over the course of two hours, according to one study. A startup that makes such a spray has gained an EPA license to sell its product to customers in the consumer, commercial, and healthcare sectors. Coatings will cost between $50 and $60 per square foot. This is an exciting technology, though a coppery finish might not be something that consumers want on every single surface. What we accept in hospital fixtures, for instance, we might not want on our phone cases.

Coatings don’t have to be copper-based, though. Last year, researchers at the University of Birmingham announced the invention of a sprayable coating derived from cellulose. This hydrophilic coating kills pathogens by drying out the respiratory droplets in which they lurk. Viruses and other microbes then become ensnared in the cellulose matrix and don’t spread as readily when touched. A material coated in the cellulose spray dries about 50 percent faster than the same volume of liquid on a glass surface. In the study, glass was coated with cultures containing infective SARS-CoV-2 particles. When the cellulose spray was applied, the size of the culture was reduced almost three-fold after 5 minutes. After 10 minutes, it was almost entirely removed.

A thin film of cellulose (MFC-I), coated onto glass, kills cells infected with SARS-CoV-2 spike protein. Droplets of virus-containing cultures were dotted onto glass or glass coated with cellulose. Infectious particles were then recovered and transferred to target cells for infection after either five or ten minutes. The blue dots are stained Vero cell nuclei. Credit: Qi S. et al. ACS Appl. Mater. Interfaces, 2023.

If this cellulose spray ever makes it to market, the invention could result in a product that’s cheap, non-toxic, and transparent, minimizing its aesthetic intrusion. Together, these qualities offer a trifecta that neither bleach nor copper can match. The spray comes off when wetted, as disinfectants do, which means that we shouldn’t use it for drinking beer with ancient Egyptians. Nevertheless, pending more research into its relative efficacy and microbes’ ability to adapt to it, cellulose spray is a technology to keep an eye on.


Whether new sprays are made using copper, carbon nanotubes, or cellulose, though, they will have to vault two hurdles: testing outside of the laboratory, and regulation. Real-world testing is tricky, especially when it comes to healthcare. Lab testing does not account for the complexity of environmental effects, where varying levels of heat and humidity can expose weaknesses in the antimicrobial performance of materials such as silver. And the outside world more generally offers challenges of its own. For the same reason that we don’t see political campaigns running as control campaigns, you’d be hard-pressed to find a hospital permitted to abandon established and effective practices for an untested alternative.

Not dissimilarly, biocidal products—those that destroy living things—must satisfy demanding regulations. During my research, I spoke to an entrepreneur who tried to build a start-up that used copper in phone cases and similar products but was brought down by the regulatory burden imposed by the European Union.3

The Biocidal Products Regulation, said Melina Gerdts, required a registration process that would have cost up to €3.5m to participate in—most of that sum being spent on testing the submitted product—and would have taken up to three years to complete. There was no clear timeline, no cost overview, and very little digitization, which means that companies have to mail their documents and wait weeks for a response. “Suddenly, the business case was not viable,” Gerdts told me.

The business case for innovative surfaces might not have been viable, but the need for them remains. Research must come first, with provable efficacy likely to lower regulatory hurdles. From there, we can imagine how things might go differently in the case of patient YY and the apartments in Amoy Gardens.

In a world more resistant to pathogens, there’d be better air purification systems, drawing in air and zapping it with far-UVC light before pumping it back into the apartments. A resilient Amoy Gardens would have better plumbing, with no route from the sewage pipes back into the bathrooms. It would also make more use—pending testing and technical progress—of modern biocidal sprays, both as a rule and in response to outbreaks. Bathrooms, kitchens, and high-touch common surfaces, such as elevator buttons and communal light switches, would be regularly sprayed with something like a cellulose-based coating. Like bleach, it would be cheap and quick; unlike bleach, it would be non-toxic, and it would not contribute to antibiotic resistance.

We can let viruses and bacteria get out of hand, or we can ensure they never make it onto our hands in the first place.


Tom Ough is a freelance journalist. His writing is generally concerned with either the enhancement of humanity’s future or the aversion of its sticky end.

Cite this essay: Tom Ough. "Blocked Transmission." Asimov Press (2024). DOI:

Correction: An original version of this essay overstated the amount of energy needed to deactivate human coronaviruses.



  1. SARS, like adenoviruses, influenza, and hepatitis A, is one type of virus that often spreads in this way.
  2. An analysis of 42 studies yielded the estimate that “approximately 19% of the world population washes hands with soap after contact with excreta (i.e. use of a sanitation facility or contact with children’s excreta).” That figure of 19% is a fraction of the 71% who, in 2020, were able to wash their hands with soap and water at home.
  3. In the United States, would-be manufacturers must seek the approval of the F.D.A. and E.P.A. This process is arduous, but Gerts views it as easier to navigate than European Union rules.
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