Highlights Social distancing index P d was developed on basis of exhaled droplet distribution and transmission. The perfect-mixing-based Wells-Riley model was modified by introducing the social distancing index P d and ventilation effectiveness E z . The safe social distance is recommended as 1.6–3.0 m considering aerosol transmission of exhaled large droplets from talking. The modified model used one actual pandemic case to calibrate the infectious dose and verified by a number of other existing cases. Projections using the validated model illustrated the efficacy of social distancing and influence factors on required ventilation rate.

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Infectious disease outbreaks and epidemics such as those due to SARS, influenza, measles, tuberculosis, and Middle East respiratory syndrome coronavirus have raised concern about the airborne transmission of pathogens in indoor environments. Significant gaps in knowledge still exist regarding the role of mechanical ventilation in airborne pathogen transmission. This review, prepared by a multidisciplinary group of researchers, focuses on summarizing the strengths and limitations of epidemiologic studies that specifically addressed the association of at least one heating, ventilating and/or air-conditioning (HVAC) system-related parameter with airborne disease transmission in buildings. The purpose of this literature review was to assess the quality and quantity of available data and to identify research needs. This review suggests that there is a need for well-designed observational and intervention studies in buildings with better HVAC system characterization and measurements of both airborne exposures and disease outcomes. Studies should also be designed so that they may be used in future quantitative meta-analyses.