One approach to COVID-19 that has been gaining traction, is the idea of decontaminating surfaces to inactivate viruses that have been deposited upon them, either by aerosols, droplets, or contaminated touch. Infection from surfaces is a major concern for public entities and private businesses such as schools, public transportation, airlines, hotels, hospitals and doctors’ offices, restaurants, gyms and cruise ships. The technical issues are not trivial. Treatments of surfaces by disinfectants must be highly effective on their antiviral activity. Additionally, they should not be too expensive; otherwise, their economic benefits in terms of reduced labor costs, lower infection rates and increased customer traffic would fail to offset costs. Safety is of significance with several approaches that have been developed, particularly in the context of SARS-CoV-2, an enveloped virus which is relatively easy to inactivate. Ideal virucides would also be effective against the more difficult, non-enveloped viruses such as norovirus, and against bacteria as well.
One general approach uses quarternary amine (QA) compounds. These contain a central nitrogen bound covalently to four hydrocarbon groups. They, thus, have both a strong positive charge and hydrophobic properties. As such, they disrupt lipid membranes through surfactant activity, attract the negatively charged surfaces of microbes and can cause protein aggregation (1). Two of the GVN’s Centers of Excellence (the Peter Doherty Institute for Infection and Immunity in Melbourne, Australia and the Rega Medical Research Institute of KU Leuven, Belgium) tested one such formulation, BioProtect, developed by ViaClean Technologies, which contains a mixture of five different QAs. When sprayed onto a surface, the QAs are covalently attached to the surface and self-assemble into nanoparticle spikes, which disinfect the surface by the typical QA activities. The covalent attachment gives the preparation durable activity that is claimed to last for at least three months. Results from both the Doherty Institute and the Rega Institute with this agent demonstrated SARS-CoV-2 inactivation of 99.7% within 10 minutes, 46 days after application, and led to degradation of the viral RNA. Another approach by Exilva uses a formulation of QAs with microfibrillated cellulose as a spray onto surfaces. The microfibrillated cellulose is not water soluble and is claimed to provide a durable coating.
A different approach covalently attaches a titanium dioxide nanoparticle photocatalyst to surfaces. The catalyst acts on water and oxygen in the presence of light to generate a variety of reactive oxygen species that attack bacteria and viruses. The product, called ACT CleanCoat, is currently being used by some cruise line operators, hotels and food processors to defend against SARS-CoV-2. Durability is claimed to be up to a year. Tests by the European Chemical Union have shown it to be effective against both enveloped and non-enveloped viruses, including MERS and murine norovirus, as judged by EN 14476 standards. This approach does, however, require that the surfaces be exposed to light.
Surface transmission of SARS-CoV-2 is certainly not a negligible concern, and such approaches could also be quite useful against other microbes, such as norovirus and bacteria. The use of advanced and durable methods for surface decontamination seems to be increasingly useful in different industries, including: academia, medical institutions, transportation, hospitality, travel, food processing and health and wellness centers.
It is clear, however, that airborne transmission, particularly in enclosed spaces, is a major route of transmission and needs to be dealt with. Masks are at least partially effective in providing protection from airborne transmission; although, they are not completely effective depending on the mask types. So how might such a problem be approached?
As evidenced by superspreading events at a choir in Washington State and a call center in South Korea, transmission powered by breath and carried in the form of droplets and aerosols are major contributors. Control of air circulation, therefore, and the decontamination from viral, airborne particles will be necessary. Heavier droplets would probably not be captured by air recirculation, and would drop to surfaces, but the approaches mentioned above for surface decontamination would rectify this. One of the ways to remove viruses and other microbes is by recirculating air through a high-efficiency particle (HEPA) filter. In fact, this is routine on commercial airliners, and is why disease transmission rarely occurs in that setting.
Another mechanism to inactivate coronavirus is far ultraviolet UVC light (207 to 222 nm), as shown by results on the cold-related human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Their biologic similarity to SARS-CoV-2 suggests that this approach should be applicable and the wavelengths used are not harmful to people. Areas that the light reaches directly could be disinfected with a limitation. Directing airflow to the closest proximity to a UVC source would be needed to maximize the virucidal effect. While surfaces that receive UVC light directly would be decontaminated, it seems that the greatest virus protection in indoor spaces would result from a combination of long-term surface decontamination combined with airflow control and UVC light/HEPA filtration.
- G. A. Knauf et al., Exploring the Antimicrobial Action of Quaternary Amines against Acinetobacter baumannii. mBio 9, (2018).