The use of ultraviolet germicidal irradiation (UVGI) in disinfection of airborne bacteria

Abstract

Contamination of indoor air by microbial pollutants has been increasingly recognized as a public health problem, and may be responsible for building-related illness (BRI) and sick-building syndrome (SBS). Bioaerosols such as fungi, bacteria, and viruses in indoor air can cause allergic and irritant responses, infectious diseases, respiratory problems, and hypersensitivity reactions. People sensitive to indoor environmental problems complain of a wide variety of symptoms ranging from headache, fatigue, nausea, sinus congestion, to eye, nose, and throat irritations.

Although ultraviolet germicidal irradiation (UVGI) with a predominant wavelength of 254 nm has been used for air disinfection for many years to minimize microbial numbers in the air, few quantitative data are available on the radiation susceptibilities of individual airborne microbes. There have been a number of UVGI studies documenting the effectiveness of UVGI for the control of microbes in controlled settings. Many of these studies documented the effectiveness of UVGI against airborne tuberculosis organisms.

The studies described here used commercial type fan-powered shielded UVGI-containing fixtures to evaluate their effectiveness in air disinfection. Aerosolization tests were done in the contained environment of a negative pressure bioaerosol stainless steel testing chamber 0.75 m wide·3.7 m long. The chamber was designed so that microbes could be safely aerosolized and contained while traversing the chamber through the UVGI-containing fix-tures. Four commercial (Purair UV Germicidal Systems, Mount Vernon, N.Y.) fan-powered UVGI-containing fix-tures placed in the chamber were individually evaluated for their ability to disinfect individual bioaerosols of air-borne bacteria.

Air samples were taken at the inlet and outlet of the UVGI-containing units positioned in the bioaerosol chamber, using Ace Glass all-glass impingers (AGI-30). Five bacterial species were individually aerosolized to evaluate their kill. The bacteria used to test all of the UVGI-containing units were vegetative cells of Escherichia coli, Micrococcus luteus, Pseudomonas fluorescens, Staphylococcus aureus, and endospores of Bacillus subtilis. Based upon the concentration of bioaerosols collected at the inlet and outlet of the fixtures tested, the total overall microbial kills for the four fixtures with the filters in place and the UVGI units on were more than 99% for all the airborne vegetative bacteria tested, and a mean of over 75% for the B. subtilis endospores.

All of the fixtures were efficient in the kill of the test vegetative bacteria used, even the more UVGI-resistant M. luteus vegetative cells and endospores of B. subtilis. Units such as these may provide an economical way to supplement existing air cleaning procedures used in indoor environments, and to kill airborne bacteria effectively without human exposure to UV light.