Overview of the Size of Respiratory Particles Containing Infectious Pathogens

TIMOTHY SIPKENS, Rym Mehri, Andrew Oldershaw, Gregory Smallwood, National Research Council Canada

     Abstract Number: 243
     Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation

Abstract
The size of respiratory particles that contain infectious pathogens is an important quantity in driving communication about specific diseases and the recommended mitigation efforts. For example, there has been discussion around whether bioaerosols, which may be associated with larger particles than other hazards like dust or soot, can have relaxed particle filtration requirements, e.g., in the context of respiratory protection for the general public. In this respect, the size dependent particle filtration efficiency of many products could then be exploited, still blocking ~99% of relevant pathogens while allowing for increased breathability by relaxing the typical sub-micron particle filtration efficiency. However, questions remain around the particle sizes relevant to disease transmission, requiring summaries of existing data on the topic. Certain aspects of the problem may be reasonably well understood. A number of recent works have provided some discussion of the droplet–aerosol distinction, including tracing its lineage, providing some discussion of its relationship to particle size, and acknowledging that there may now be a shift in thinking about disease transmission (Jimenez et al, 2021; Randall et al, 2021). The size range of human-generated aerosols has also seen a fair amount of study, see Bourouiba (2021). Even in this case, data will naturally contain uncertainties due to human factors. Some recent work has also summarized some aspects of these transmission pathways, in particular for viruses (Wang et al, 2021). Here, we supplement these studies with a summary of the state of knowledge with an explicit focus on particle size, including identifying persisting gaps that remain in the literature and spanning across a broader range of pathogens. Hereby, we identify future research avenues to close some of the gaps, and to aid policymakers in better responding to future and existing respiratory infectious diseases.