Airborne transmission of infectious agents resulting in disease has been well-documented. There has been renewed interest in applying engineering controls to remove or inactivate causative agents. Engineering controls include direct source control using local exhaust ventilation, maintenance of negative pressure differences between isolation/treatment rooms and adjacent areas, dilution and removal of contaminated air via mechanical ventilation, in-room air filtration, ultraviolet germicidal irradiation (UVGI), and using respiratory protective equipment. These controls are designed to reduce the concentration of infectious agents within the local environment, to protect those who come into close contact with infectious persons, and to prevent spreading of infectious agents.

For upper-room air UVGI, germicidal lamps are suspended from the ceiling or attached to the walls; the bottom of the lamp is usually shielded or louvered to direct radiation upward above a predetermined height. The objective of this configuration is to inactivate airborne infectious agents in the upper part of the room, while minimizing radiation exposure to persons in the lower part of the room. Inactivation in this context means the loss of the ability to replicate and form colonies. Commercially available germicidal lamps contain mercury vapors under low pressure that emit nonionizing electromagnetic radiation in the UV-C wavelength range, 100-290 nm, with about 90% of the total spectral power emitted at 254 nm. UVGI that penetrates to microbial DNA may cause damage sufficient to interrupt cell replication.

Studies have been performed evaluating the effectiveness of upper-room air UVGI to inactivate bioaerosols. Upper-room UVGI has been shown to inactivate airborne bacteria at significant rates and it has been shown to be effective in controlling a number of airborne biological contaminants.

Kujundzic, E., Matalkah, F., Howard, D. J., Hernandez, M., and Miller, S. L., Air cleaners and upper-room air UV germicidal irradiation for controlling airborne bacteria and fungal spores, Journal of Occupational and Environmental Hygiene, 3:536-546, 2006.

Kujundzic E, Miller SL, Hernandez M. Ultraviolet germicidal irradiation inactivation of airborne fungal spores and bacteria in upper-room air and HVAC in-duct configurations. J. Env. Eng. Sci. 2007; 6:1-9.

Macher, J.M., Alevantis, L.E., Chang, Y.-L., and Liu, K.-S. 1992. Effects of ultraviolet gernicidal lamps on airborne microorganisms in an outpatient waiting room. Appl. Occup. Environ. Hyg., 7: 505-513.

Miller, S.L., and Macher M.J. 2000. Evaluation of a methodology for quantifying the effect of room air ultraviolet germicidal irradiation on airborne bacteria. Aerosol Sci. Technol., 33: 274-295.

Xu, P., Peccia, J., Fabian P., Martyny, J.W., Fennelly, K.P., Hernandez, M., and Miller, S.L. 2003. Efficacy of ultraviolet germicidal irradiation of upper-room air in inactivating airborne bacterial spores and mycobacteria in full-scale studies. Atmospheric Environment, 37: 405-419.

Xu, P., Kujundzic, E., Peccia., J., Schafer, M., Moss, G., Hernandez, M., and Miller, S.L. 2005. Imapact of environmental factors on efficacy of upper-room air ultraviolet irradiation for inactivating airborne Mycobacteria. Environ. Sci. Technol., 39: 9656-9664.