Efficacy of Portable Filtration Units in Reducing Aerosolized Particles in the Size Range of Mycobacterium tuberculosis

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Abstract
Objective: To evaluate engineering control measures to prevent nosocomial transmission of diseases such as tuberculosis, we studied four portable high-efficiency air filtration units, including three high-efficiency particulate air (HEPA) filtration units, for their ability to remove aerosolized particles. Design: Studies were conducted in either a nonventilated aerosol chamber or in a hospital isolation room that met CDC guidelines for TB control (negative pressure, ≥ air changes per hour, air exhausted directly to the outside). The rooms were challenged with aerosolized mineral oil in the size range of 0.3 to 5.0 µm at levels 10 to 20 times the normal airborne particle load in the room at baseline. Airborne particles were counted with a laser counter capable of simultaneously measuring sizes ≥0.3, ≥0.5, ≥1.0, and ≥5.0 µm. Experimental runs were conducted with the filtration units in the center or corner of the chamber or room, and the particle counter in the center of the room or at the exhaust vent. Results: Portable filtration units were effective in accelerating the removal of aerosolized submicron particles. In the nonventilated room, time required by the various portable filtration units for removal of 90% of aerosolized particles (≥0.3 µm) ranged from a low of 5 to 6 minutes to a high of 18 to 31 minutes, compared to the control (no filtration unit), >171 minutes. In the hospital room, individual filtration units removed 90% of aerosolized particles (≥0.3 µm) in times ranging from 5 to 8 minutes to 9 to 12 minutes, compared to the control (no filtration unit), 12 to 16 minutes. The location of the portable filtration unit (center versus corner) did not affect the clearance rate of airborne particles. Conclusion: Our data indicate that portable filtration units can rapidly reduce levels of airborne particles similar in size to infectious droplet nuclei and, therefore, may aid in reducing the risk of tuberculosis exposure.