10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Influence of HVAC Operation on the Dissemination Pattern of Aerosolized Simulant Pathogen Particles in a Clinical Bio-Containment Unit
David Drewry, JENNIFER THERKORN, Thomas Pilholski, Gregory Bova, Kathryn Shaw-Saliba, Lauren Sauer, Brian Garibaldi, Johns Hopkins University Applied Physics Laboratory
Abstract Number: 359 Working Group: Infectious Bioaerosol
Abstract The Johns Hopkins Hospital Bio-Containment Unit (BCU) is a state of the art facility to care for patients infected with high consequence pathogens, such as Ebola, SARS and multidrug resistant tuberculosis. Despite the high-risk nature of the work, there is currently limited guidance on the care of patients, emergency operating protocols and facility design for BCUs. Further, the role of air ventilation in the airborne transmission of nosocomial infection is still poorly understood. In this study, the influence of HVAC operating conditions on the dissemination of released pathogen particle simulants was investigated in the Johns Hopkins BCU. Test conditions included normal HVAC operation, and the loss of negative pressure during simulated HVAC exhaust failure. A suspension of optical brightener powder in water was nebulized by 3-Jet Collison Nebulizer to produce a polydispersed particle number size distribution ranging from 0.5-5 µm (i.e., simulant for droplet nuclei particles and a range representing high consequence airborne pathogens). The dissemination pattern and concentrations of the fluorescent particles were monitored by an array of eight fluorescent optical sensors (IBACs, FLIR Systems) located throughout selected areas of the BCU. During normal HVAC conditions, the released particles were contained in the patient isolation room with an average concentration of 1x104 ± 3x103 PPL, and a maximum peak concentration of 5x104 PPL. Since there were no particles detected outside of the isolation room, this suggests that the locations and ventilation rates used by the patient room exhaust vents are sufficient to maintain airborne isolation conditions under static test conditions (i.e., with no healthcare workers or patient care activities conducted in the BCU). Under HVAC exhaust failure conditions, air flow in the patient room was reduced approximately 96% to 10 ± 3 CFM. Fluorescent tracer particles were detected in areas adjacent to the patient isolation room, including the personal protective equipment (PPE) doffing room and the main BCU corridor hallway. About 14% of the fluorescent particles detected in the patient room were transported into the doffing space. Since air movement with 1 m/s velocity was observed to flow in the direction out of the patient room through spaces around the door handles, it is hypothesized that particles were transported out of the isolation room via this route. Future research will further characterize the particle size dependent penetration factors through and around the patient room doors under different HVAC operating conditions (i.e., under different pressure differentials between the adjacent BCU rooms). Overall, this study provides a systematic method for evaluating airborne infection mitigation protocols in the BCU and suggests further steps to avoid healthcare worker exposure to high risk pathogens.