Antimicrobial air filters could drastically cut Covid spread on trains

The technology can kill an array of bacteria, fungi and viruses in seconds including providing a potential solution to prevent the spread of airborne infections.

The air filters, which are coated with a chemical biocide called chlorhexidine digluconate (CHDG), were rigorously tested and compared to commonly used standard ‘control’ filters in the laboratory, in industrial air condensing units, and in a trial onboard trains operating on the UK’s railways.

In the laboratory, Covid-19 cells were added to the surface of both the treated and control filters and measured at intervals over a period of more than an hour. 

The results showed that, while much of the virus remained on the surface of the control filter for an hour, all the Covid cells were killed within 60 seconds on the treated filter. 

Similar results were seen in experiments testing bacteria and fungi that commonly cause illness in humans – including E. coli, S. aureus, and C. albicans.

In order to determine how effective the filters are in a real-world setting, both the control and treated filters were installed in heating, ventilation and air conditioning systems on train carriages.

The filters were installed for three months in matched pairs across carriages on the same train line, before being removed and shipped for analysis, with researchers counting colonies of bacteria remaining on them.  The trial found no pathogens survived on the treated filter, even after three months on-board the train.

Further tests also found the treated filters are durable, and are able to maintain their structure and filtration function over the lifetime of their use.

Dr Felicity de Cogan, a researcher at the University of Birmingham, said: “In crowded spaces, from offices to large indoor venues, shopping malls, and on public transport, there is an incredibly high potential for transmission of Covid-19 and other viruses such as flu.

“Most ventilation systems recycle air through the system, and the filters currently being used in these systems are not normally designed to prevent the spread of pathogens, only to block air particles.

“This means filters can actually act as a potential reservoir for harmful pathogens. We are excited that we have been able to develop a filter treatment which can kill bacteria, fungi and viruses – including SARS-CoV-2 - in seconds. This addresses a global unmet need and could help clean the air in enclosed spaces, helping to prevent the spread of respiratory disease.”

While other filters have been developed in the past, the researchers believe that theirs has improved energy efficiency and is much faster working.

“In comparison, the technology we have developed can be applied to existing filters and can be used in existing heating, ventilation and air conditioning systems with no need for the cost or hassle of any modifications,” Dr de Cogan added. “This level of compatibility with existing systems removes many of the barriers encountered when new technologies are brought onto the market.”

Partner firm NitroPep is now further developing the filters to deliver them as a product on the market.