Indoor and outdoor air contains suspended biological particulate matter (bioaerosols) that can pose a threat to public health. Airborne transmission of infectious agents resulting in disease has been well documented. Efforts to design and optimize appropriate systems to remove or inactivate causative agents are underway. Transmission of Mycobacterium tuberculosis is a classic example of airborne contagion. The possibility for adverse health effects associated with bioaerosols including disease transmission has prompted an effort to design appropriate systems and methods to remove causative agents. The Centers for Disease Control and Prevention (CDC) specifies a combination of administrative, engineering, and personal respiratory protection measures to achieve infection control. Engineering controls include direct source control using local exhaust ventilation, maintenance of pressure differences between isolation/treatment rooms and adjacent areas, dilution and removal of contaminated air by mechanical ventilation, in-room air filtration, and ultraviolet germicidal air irradiation (UVGI). These controls are designed to reduce the concentration of bioaerosols within the local environment, to protect those who come into close contact with infectious persons, and to prevent bioaerosols from spreading throughout a facility. Despite the fact that filtration has been used to reduce indoor pollutant concentrations in many settings, and that filtration has been shown to be effective in controlling a number of indoor airborne contaminants, little is known about the use of filtration with regard to decreasing the risk of infectious diseases. There is also a need to explore the effectiveness of combining filtration with other engineering controls such as UVGI. Information on the efficacy of engineering controls is needed to provide a rational basis for developing strategies for reducing the transmission of infectious diseases. For many of the control strategies, there are numerous factors that can influence their performance, and information on their efficacy is lacking. To assess the impact of control strategies that target airborne infectious agents, it is necessary to challenge them with a bacterial aerosol similar to those that transmit diseases in realistic settings. The overall objective of this study was to conduct experiments to quantify the rates at which bioaerosols are removed and/or inactivated by three portable air cleaners (PACs), and by the P ACs combined with the operation of an upper-room air UVGI system. Filtration has been used to reduce indoor pollutant concentrations in many settings and it has been shown to be effective in controlling a number of airborne contaminants. Chamber studies have been performed evaluating the efficiency of PACs challenged with biological and non-biological aerosols. Commercially available low-pressure mercury-vapor lamps used for UVGI applications emit nonionizing electromagnetic radiation with a predominant wavelength of 254 nm. UVGI that penetrates to microbial DNA may cause damage sufficient to interrupt cell replication. UVGI can be used for air disinfection in an open configuration irradiating room air. Studies have been performed evaluating efficiency of UVGI to inactivate bioaerosols. Transmission of infectious diseases, such as TB, through inhalation of airborne bacteria is a public health problem that may pose substantial risks to healthcare workers and a general risk to tl1e public. Air filtration and applied UVGI are engineering control methods that can prevent the spread of bioaerosols through indoor environments. Observed and reported data showed that it is essential to ensure a low risk for transmission of infection through high-risk settings. The experimental results of this study showed that filtration alone and in combination with UVGI can remove/inactivate airborne bacteria at reasonable rates. Equivalent air-exchange rates in the range of 5-12 ACH can be achieved using P ACs, depending on the type of air cleaner. Additionally, one air cleaner tested did not have any effect on airborne bacteria (NIG). These air-exchange rates are comparable with previous studies. Operating UVGI in conjunction with the P ACs added an additional 7-17 ACH, depending on the number of lamps operating. This additional equivalent air-exchange rate due to UVGI is comparable with previous studies. Completion of the proposed research significantly improved our understanding of the efficacy of PACs and combination of PACs and UVGI against biological aerosols. Observed data showed that portable cleaners could be used to enhance the rate ofbioaerosol in-activation due to UVGI and vice versa.
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