Case studies using a simple airborne infection risk calculator to minimize COVID-19 infection risk: Common approaches and challenges

Following the recognition of the role of airborne transmission in the spread of SARS-CoV-2, the role of building ventilation in minimising indoor respiratory events has become of significant interest, with numerous risk assessment tools developed to understand infection risk in different indoor environments. To date there has been limited retrospective analysis of how such tools were applied to assess indoor infection risk and inform building occupancy during the COVID-19 pandemic. In this paper we document case studies from Australia and New Zealand using one such risk assessment tool, the Airborne Infection Risk Calculator (AIRC), and describe how the AIRC was used to assess COVID-19 risk in different indoor settings and how users customized the tool for their own purposes. While inherent uncertainties mean the AIRC model could not calculate the exact risk in any of the case studies, the model's framework enabled objective discussion about the role of ventilation in infection risk reduction and public health. Future use of tools such as the AIRC would be improved with development of policies or regulations that promote or require a standardized approach for this assessment, translation of improvement in ventilation in a room or building scale into overall public health benefits, and endorsement of such tools by Global and/or National health authorities.