Evaluation of a Methodology for Quantifying the Effect of Room Air Ultraviolet Germicidal Irradiation on Airborne Bacteria

Abstract

ABSTRACT. As a result of the recent resurgence in tuberculosis (TB) and the increasing incidence of multidrug-resistant TB, there has been renewed interest in engineering controls to reduce the spread of TB and other airborne infectious diseases in high-risk settings. Techniques such as the use of lamps that produce ultraviolet germicidal radiation may reduce exposure to infectious agents by inactivating or killing microorganisms while they are airborne. We designed and evaluated a test method to quantitatively estimate the ef cacy of germicidal lamps, in conjunction with dilution ventilation, for reducing the concentration of viable airborne bacteria. Bacterial particles were generated in a 36 m 3 room and collected with midget impingers at 5 -7 locations. The effectiveness of the control technique was determined by comparing concentrations of culturable airborne bacteria with and without the control in operation. Results for a single, 15 W germicidal lamp showed reductions of 50% for Bacillus subtilis (B. subtilis) and Micrococcus luteus (M. luteus); tests with Escherichia coli (E. coli) showed nearly 100% reduction (E. coli were isolated only from the sampler nearest the aerosol source when the lamp was operating). The addition of louvers to a lamp greatly reduced its ef cacy. Decay experiments showed that roughly 4 -6 equivalent air changes per hour were achieved for B. subtilis with one or two lamps operating. These preliminary experiments demonstrated that this methodology was well suited for these evaluations and identi ed factors that could be modi ed to re ne the study design for future work.

Development of a Protocol for the Determination of the Ultraviolet Sensitivity of Microorganisms Suspended in Air

“…The fac- tors that affect the distribution of the fluence rate inside the quartz cell can be determined precisely by applying the protocol to the reactor. In contrast, the geometries used by other researchers (Fletcher et al 2003;Miller and Macher 2000;) are more complex and the fluence rates were either measured by carrying out actinometry at certain spatial points , or by a series of radiometer measurements within the UV reactor (Miller and Macher 2000). With these approaches many measurements must be made, and it is hard to determine the appropriate number of and location of the points where measurements should be made in order to calculate the average fluence rate of the reactor accurately.…”

“…The volume of the quartz-capped vessel apparatus is relatively small (1.5 L) compared to apparatuses used by other researchers (Fletcher et al 2003;Miller and Macher 2000;. A small vessel is preferred in bioassay testing, especially when pathogenic microorganisms are the study objects, since it is easier to control possible leakage of the microorganisms into the environment.…”

“…The lack of a standard protocol makes it difficult to compare the findings of the various studies and to develop rigorous system design methodologies. Table 1 illustrates the diversity of methods and apparatuses that have been used in recent aerosolized microorganism UV inactivation studies (Fletcher et al 2003;Miller and Macher 2000;Xu et al 2003).…”

“…Because it is a nearly ideal well-mixed batch reactor system, the UV inactivation constants determined using this apparatus and protocol are fundamental properties of the microorganism and are independent of the fluid flow regime and reactor geometry. This reactor (Fletcher et al 2003) Pilot scale flow through chamber (4 L) Radiometer reading through an access port to estimate the irradiance (Miller and Macher 2000) Completely mixed room (36 m 3 ) with ventilation 12 point radiometer readings to estimate the average fluence rate (Ko et al 2000) Flow through UV chamber (7.3 L) 90 point radiometer readings to calculate the average fluence rate (Xu et al 2003) Completely mixed room (87 m 3 ) with ventilation 20 spherical actinometry cells (1 cm diameter) and radiometer readings independency is of great value in UV reactor design, especially when Computational Fluid Dynamics (CFD) simulation techniques are used to model the fluid flow in larger, continuous-flow reactors.…”

Effects of Ceiling-Mounted HEPA-UV Air Filters on Airborne Bacteria Concentrations in an Indoor Therapy Pool Building

“…Ultraviolet (UV) radiation and high-efficiency particulate air (HEPA) filtration of indoor air have received heightened attention in recent years as effective and affordable engineering controls. [13][14][15][16] Above certain dose levels, UV radiation at the 254-nm wavelength has been shown to inactivate airborne bacteria. Experimental and anecdotal evidence suggest that UV irradiation may be an effective IMPLICATIONS Transmission of infectious diseases through inhalation of airborne bacteria, viruses, or fungi is a public health problem that may pose substantial risks to the general public.…”