Recently, a stellar panel of engineers and infectious disease experts—representing about “150 years of learning”— virtually gathered for a webinar to talk about the safety and evidence base supporting the use of upper air ultraviolet germicidal irradiation (UVGI or UV), also known as upper room germicidal ultraviolet light (UR-GUV). Hosted by a consortium of leading institutions including the Harvard Kennedy School and Harvard Global Health Institute, the online presentation, Keeping Public Spaces Safe: Germicidal Ultraviolet Light for Air Sanitation During COVID-19, addresses “an urgent need for a digestible overview of the state of the science of upper room UVGI and how that can apply to the fight against COVID-19 and other future threats.”

As noted in the presentation, like COVID-19, which is “passed through the air through droplets and aerosols,” tuberculosis (TB) is an airborne disease, and some of the principles that have been used for TB could be used for creating safe public spaces today in the wake of COVID-19. Further, upper room germicidal lighting is something that “we know works and doesn’t rely on individual behavior” like wearing masks and social distancing (although those behaviors are still important).

One of the questions from the audience at the end of the webinar led to an answer from Dr. Milton (more on him, below) that really drives home the importance of eliminating aerosolized pathogens in the air, before they can be inhaled, to reduce the spread of infectious disease. Summarizing that Q&A:

Q: What percent of airborne particles reach the upper room and what percent land and linger on fomites (surfaces)?

A: While we don’t know the specifics yet of SARS-CoV-2 (the virus that causes COVD-19), we do know well from influenza studies that it takes a single influenza virus to deposit deep in the lung to cause full-blown flu with fever, chills, and systemic symptoms. But it takes 100,000 influenza viruses placed n the nose to cause mild upper respiratory infections with no fever and to get those massive numbers of viruses into your nose by touching surfaces is, in short, extremely difficult.

The webinar is about an hour and a half long and well worth the time investment, but we’ve also put together a summary of presenter sessions, below, with at least two key takeaways from each.

Is UVGI safe?

Highlights from the “Introduction & Safety of UVGI” presentation by David Sliney, PhD, a biophysicist and consulting medical physicist.

With regard to using UV and safety, Dr. Sliney says: “UV germicidal irradiation can be safely and effectively used for upper air disinfection without significant risk for long term delayed effects such as skin cancer.” He addresses the use of louvres to direct UV into the upper space (e.g., our Zone360 and Zone180 are designed with louvres).

Two additional key takeaways from his presentation:

• Emphasizing the importance of proper installation, Dr. Sliney says: “When appropriately designed and installed, UVGI technology has been an effective means of microbial disinfection.”
•  “UVGI offers about the only method for air disinfection (other than gas, which cannot be used with unprotected persons present in the space).”

How are respiratory infections transmitted?

Highlights from the “How Respiratory Infections are Transmitted” presentation by Donald Milton, MD, DrPH, Professor of Environmental Health, Applied Environmental Health (MIAEH) Affiliate in Cell Biology and Molecular Genetics; Professor, Internal Medicine, University of Maryland School of Medicine.

Dr. Milton addresses the transmission modes of respiratory viruses, how respiratory particles are generated, and how SARS-CoV-2 is spread by aerosols. He  shares a study of a hospital room air where samplers were placed on either side of the room; samplers picked up culturable virus demonstrating it had traveled across the room.

Also discussed are thoroughly scrutinized restaurant outbreaks which showed air going in a loop. In one South Korea restaurant people as far as 21 feet away were infected by a person with virus. For the study, among other tactics to confirm how the disease was spread, researchers watched video footage from a security camera installed in the restaurant showing that the “index case” (the person with COVID-19), never went near the others who were infected.

Two additional key takeaways:

• With regard to how SARS-CoV-2 is spreading in settings like those described in the restaurant study, Dr. Milton says, “this can only be happening by aerosols.”
• Dr. Milton further notes that SARS-CoV-2 can survive in the air for at least 16 hours as demonstrated by a study conducted in New Orleans with about 50% humidity and at 23° C (73.4° F). At 16 hours, he says, this is much longer than ventilation would remove it from the air.

How does upper room UVGI work and where can it be used?

Highlights from the “Theory and Application of Upper Room UVGI” presentation by Edward Nardell, MD, Professor of Medicine at Harvard Medical School and Harvard School of Public Health.

Dr. Nardell recounts his first experience with the use of UV for an outbreak of TB at a homeless shelter in the 1980s. As he explains, UV is not a new technology. He references “Applications of Germicidal, Erythemal and Infrared Energy” by Dr. Matthew Luckiesh, published in 1946, which even then was not new technology, as well as the famous real-world application and study by William F. Wells of using upper room UVGI to prevent the epidemic spread of measles among children in suburban Philadelphia day schools. Another interesting study Dr. Nardell shares is a 1957-1958 study at a VA hospital in Livermore, California. The observational study showed that in rooms where UV had been installed to help prevent the spread of TB, the rate of seasonal flu was a fraction of that in rooms where UV was not installed. Although not a planned or controlled study, Dr. Nardell said it was “rather convincing evidence” of UV being about 90% effective.

For his presentation, Dr. Nardell also addresses the use of fans to help ensure good air mixing in a room to improve efficacy of UV. While UV works without fans, he says, the better the air mixing the better the air disinfection. (Note: Aerapy’s upper air UV units all feature built-in fans to help ensure effective air mixing). Later in the webinar during the Q&A session, Dr. Milton describes a scenario where ceiling fans were recommended to improve air mixing but that would double the cost of the project. But, he says, by doubling the cost you’re also getting a 5 or 10 fold increase in effectiveness of the UV.

Dr. Nardell also discusses a study of cost effectiveness that pitted ventilation against three different room air cleaners versus UVGI and an interesting study, “Monitoring Human Exposures to Upper-Room Germicidal Ultraviolet Irradiation,” which addresses UV safety.

The three big takeaways from Dr. Nardell’s presentation are:

• “Upper room UV is, by far, the most efficient method of air disinfection for those rooms where it is feasible.”
• “Upper room UV is safe for room occupants.”
• As described, above, using fans with UV offers better air mixing for increased air disinfection.

How is upper room UVGI part of a total building infection control program?

Highlights from the “Integrating GUV as Part of the Total Building Infection Control” presentation by William Bahnfleth, PhD, a professor of architectural engineering at Penn State and a fellow of American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the American Society of Mechanical Engineers (ASME) and the International Society for Indoor Air Quality and Climate (ISIAQ).

Dr. Bahnfleth notes that “SARS-CoV-2 RNA has been found throughout HVAC systems…found on pre-filters, final filters, and supply air dampers.” Two key takeaways from his presentation:

• “Additive” air cleaners such as ionizers are being “heavily promoted” but there is limited evidence of effectiveness and incomplete evidence of safety.
• Upper room UV seems to be a good application in densely occupied spaces such as lunchrooms, restaurants, auditoriums. Upper room UVGI, he says, “can be an important supplementary control.”

 How to use upper room UVGI?

Highlights from the “Practical Application of Upper-room UVC Systems” presentation by Paul Jensen, PhD, who retired last year after more than 30 years with the Centers for Disease Control and Prevention (CDC).

Dr. Jensen explains his approach to risk assessment and facility assessment. His considerations for both are the two key takeaways (and supports why Aerapy says there is no “one size fits all” solution when it comes to UV).

• For risk assessment he looks at microorganisms of concern, who are the clients and what are their needs, and what infection control plan or program is currently in place.
• For facility assessment, he looks at the practical aspects of implementation of upper room UVGI including ceiling heights, any limitations due to activities to be conducted in the space, available electricity, and how much air mixing is possible through existing HVAC and fans.

Thank you to this remarkable group of experts for presenting this “digestible overview of the state of the science of upper room UVGI and how that can apply to the fight against COVID-19 and other future threats” and to the hosts for making it free for all to watch and learn from. For those interested in watching the entire webinar, you can do so online here.  

Photo, above, Aerapy’s upper air UVGI unit, Zone360, installed in fire department classroom.