Germicidal air disinfection in the time of coronavirus
Ed Nardell, MD
Professor of Global Health and Social Medicine, Harvard Medical School
Professor, Dept of Environmental Health and Dept of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health
Date: June 15, 2020
Time: 1:00 – 2:00 pm
Location: https://harvard.zoom.us/j/95178721732 (no prior registration required)
Abstract: Germicidal UV air disinfection has been in use for nearly a century. In the 40’s Wells, who began his work on airborne infection at Harvard, showed that UV in schools greatly reduced measles transmission. But with the advent of vaccines and antibiotics, public health motivation waned to control respiratory infections by decontaminating indoor air – akin to controlling waterborne illnesses where UV remains a standard. With the HIV-related resurgence of TB in the US between 1985-1992, interest in UV air disinfection increased, for example, in hospitals, homeless shelters, and prisons. It also drove research (mostly at HSPH) on the evidence-based, safe implementation of this technology. The 2006 outbreak of extensively drug resistant TB in South Africa resulted in international spread of upper room UV technology. Conventional mercury vapor 254 nm wavelength UV lamps can be used to disinfect air in ventilation ducts, room air cleaners, surfaces of unoccupied rooms, and air in occupied rooms using upper room fixtures and air mixing. By far the most useful is upper room UV air disinfection in occupied rooms where upwards of 20 equivalent ACH can be added. Due to limited skin and eye penetration, occupant safety is not a major issue. The Covid-19 pandemic has renewed interest in this technology – and have stimulated rapid development of two new UV air disinfection technologies: 222 nm Far UV and LED UV, 265-270 nm, and potentially 222 nm. While still germicidal, 222 nm UV cannot penetrate the outer layer of skin or eye to cause irritation – allowing direct irradiation of occupied rooms. It may have limited ability to disinfect high-touch surfaces. LED UV will eliminate mercury vapor lamp disposal, allow battery backup and solar power, and more flexible fixture designs – allowing integration with high-end decor. Advancements, potential applications, barriers, and limitations of UV air disinfection technologies will be discussed in detail.
Biographical Sketch: Professor Ed Nardell’s interest in airborne transmission began in the 80s with his work as TB Control Officer for Boston and the Commonwealth of Massachusetts, while also chief of pulmonary medicine at the Cambridge Hospital. Outbreaks in a welfare office building in Chelsea and a homeless shelter in Boston provided an opportunity to estimate the limitations of building ventilation in reducing transmission, and the potential for germicidal UV to have greater impact – but with its own limitations. In responding to the homeless shelter outbreak he consulted Richard Riley, student of William Firth Wells – both pioneers in our understanding of airborne infection and its control. He was instrumental in securing funding to install germicidal UV fixtures in the homeless shelter over the objections of another Boston Lung Association Board member, Professor Melvin First – “unless we study it”! There began two long-time relationships with giants in the field of airborne transmission and air quality, respectively. A major 5-city placebo-controlled study of germicidal UV in homeless shelters was ultimately inconclusive because of too little transmission, but resulted in the largest experience to date in upper room application under a wide range of buildings, and established no more eye or skin complaints than under placebo fixture conditions. Sol Permutt, Riley’s protege at Hopkins, suggested a controlled study of UV efficacy using Well’s classic human-to-guinea pig natural transmission model. The Airborne Infections Research (AIR) facilities opened near Pretoria, South Africa in 2005, providing unique resource over the last 15 years for studying UV efficacy, the efficacy of face masks on patients, room air cleaners, BCG-immunization to prevent infection, and to document the phenomenon of transient TB infection as a normal part of TB pathogenesis. Funding has been through NIOSH, NIH, and Fogarty. Fogarty fellows at HSPH and in South Africa under Steve Rudnick’s supervision advanced our understanding of upper room 254 nm UV dosing, fixture design, and safety. Much of the knowledge gained on germicidal UV is directly applicable to SARS-Covid-2 transmission, and the pandemic has accelerated rapid development of Far UVC (222 nm) and LED UV sources.