Clearing the Air: The Theory and Application of Ultraviolet Air Disinfection

Abstract

Abstract In the 1940s and 1950s, both the potential and the problems of interrupting transmission of airborne infection with ultraviolet (UV) light were demonstrated. William F. Wells first introduced the concept of droplet nuclei as the vehicles of airborne transmission and later showed that these nearly naked, suspended organisms were highly susceptible to inactivation by UV light of 254 nm wavelength (1, 2). Of the many infectious organisms that are susceptible to UV, most attention has been focused on measles and tuberculosis (TB) because of their importance as airborne infections and because each has characteristics favorable for epidemiologic study. In his classic experiment of 1942, Wells used UV light in schools to prevent the epidemic spread of measles (3). However, the inability of others to repeat Wells' success led to disillusionment (4, 5). Antiultraviolet sentiment was further fueled by concern about ozone production (negligible with current 254 nm wavelength bulbs) and by concerns about skin and eye irritation. The hope that chemotherapy would eradicate TB and that immunization would control most contagious viral illnesses may have also contributed to the near abandonment of UV. However, more than 40 years after the introduction of streptomycin, TB remains a worldwide problem and is increasing among certain populations in the United States and elsewhere, primarily in association with the acquired immunodeficiency syndrome (AIDS) (6). Reports of TB transmission among the elderly in nursing homes and among the homeless in shelters have reminded us of the potential for spread of this disease in these and other indoor environments. Less well documented, but of potential importance, is the transmission of TB and other airborne infections in jails, prisons, hospital intensive care units, and rooms used for bronchoscopy, sputum induction, and aerosol therapy with pentamidine and other agents (7–10). Close living situations like shelters and jails defy adequate control by conventional measures, but they may be benefited by UV air disinfection (11). Years after the introduction of an effective vaccine, measles still occurs, and in this country, transmission is increasingly associated with health care facilities (12). The ongoing need for improved control of person-to-person airborne transmission of some respiratory infections, our increasing reliance on recirculated air, and our growing understanding of where UV air disinfection is likely to work have prompted this review. Because UV must be properly planned and installed to be effective and safe, we will deal first with the theoretic and technical aspects, then we will deal with the selection of settings where we believe air disinfection should find application.