PROJECT SUMMARY Accurate assessment of healthcare workers’ personal exposure to airborne pathogenic viruses is hampered by existing bioaerosol samplers, which are either inefficient in sampling infectious airborne viruses and maintaining their viability, or not suitable for personal sampling. The goal of this proposed work is to more accurately assess personal exposure resulting from different transmission modes of airborne infectious viruses. This will be accomplished by empowering the National Institute for Occupational Safety and Health (NIOSH) bioaerosol sampler to be the personal sampler of choice so that it can efficiently collect airborne virus-containing particles by their particle size and maintain their viability information for exposure risk assessment. The two specific aims of this proposal are to: (1) Calibrate the NIOSH sampler against the gold- standard reference of Viable Virus Aerosol Sampler (VIVAS). The VIVAS is highly efficient in collecting viable airborne viruses, but too large and heavy for personal sampling. The calibration will be conducted using lab-generated respiratory virus aerosols to obtain correction factors for determining viable virus aerosol concentrations using the NIOSH sampler. (2) Evaluate personal exposures of healthcare workers to airborne viruses using the calibrated NIOSH sampler. Field tests of co-located NIOSH sampler and the VIVAS at a student health care center (SHCC) will corroborate the lab-generated correction factors in a real-world environment. Sampling will then be conducted using the calibrated NIOSH sampler to assess the personal exposures of the receptionist, healthcare providers, and medical assistants at the SHCC during flu season. Results of the size-fractionated virus-containing particles collected by different stages of the NIOSH sampler will bring to light the relative importance of the different transmission modes of airborne viruses. Paired comparisons of the personal vs. stationary samplings will reveal if stationary sampling can substitute for personal sampling. Knowledge learned from the proposed study will allow setting of administrative polices and engineering control that better protect healthcare workers from undesired exposure to airborne infectious viruses. This proposal responds to two goals set by NIOSH’s Strategic Plans for FY 2019-23 that best represent the health and safety issues facing the U.S. workforce: Goal 3 - reduce occupational infectious disease, and Goal 5 - reduce occupational respiratory disease. Specifically, Goal 3.3 - infectious disease transmission, and Activity Goal 3.3.1 - conduct basic/ etiologic research to better understand influenza aerobiology and transmission in healthcare settings.