key: cord-0949560-fvkwxfwk authors: Duchaine, Caroline; Roy, Chad J. title: Bioaerosols and airborne transmission: Integrating biological complexity into our perspective date: 2022-02-24 journal: Sci Total Environ DOI: 10.1016/j.scitotenv.2022.154117 sha: 3c2c73083c9c84045a5416b57d1e859074f3fe01 doc_id: 949560 cord_uid: fvkwxfwk There is broad consensus that airborne disease transmission continues to be the thematic focus of COVID-19, the complexities and understanding of which continues to complicate our attempts to control this pandemic. Masking used as both personal protection and source reduction predominates our society at present and, other than vaccination, remains the public health measure that will faithfully reduce aerosol transmission and overall disease burden (Gandhi and Marr, 2021). Early in the advent of the COVID-19 pandemic, and especially after preliminary recognition of airborne transmission, there was considerable efforts in the application of computational fluid dynamics (CFD) modeling aerosols as well as risk models calculations, the products of which were detailed in the literature (Morawska et al., 2020; Buonanno et al., 2020a) and even disseminated in media destined for the public. As the respiratory pathway emerged as the dominant exposure pathway for SARSCoV-2 transmission, much of what was promoted from CFD was applied to risk models to estimate community infection and in some cases expected clinical outcome. COVID-19 proved to fit the profile of an obligate respiratory-transmitted pathogen, and the plausibility of using aerosol modeling when silhouetted with emerging COVID-19 epidemiology provided ample evidence for promotion of masking and ventilation optimization as a required public health measure. Masking is often included as a factor in developed risk models and it remains an essentially important part of our response to this airborne threat, and ultimately will agnostically reduce disease burden although efforts to improve ventilation in indoor spaces remain a challenge. Arguably the most important concept in the airborne transmission of infectious agents is the biologically active componentry that comprises the aerosol particle and the functional dynamic nature of particle contents. Specifically, the innate generation, transport, and ultimate deposition/disposition of bioaerosols; the aerosol particles that nearly exclusively harbor bioactive components, including viruses, when disease agents are transmitted through the air. Caroline Duchaine, Ph.D. and Chad J. Roy, Ph.D., M.S.P.H. There is broad consensus that airborne disease transmission continues to be the thematic focus of COVID-19, the complexities and understanding of which continues to complicate our attempts to control this pandemic. Masking used as both personal protection and source reduction predominates our society at present and, other than vaccination, remains the public health measure that will faithfully reduce aerosol transmission and overall disease burden 1 . Early in the advent of the COVID-19 pandemic, and especially after preliminary recognition of airborne transmission, there was considerable efforts in the application of computational fluid dynamics (CFD) modeling aerosols as well as risk models calculations, the products of which were detailed in the literature 2,3 and even disseminated in media destined for the public. As the respiratory pathway emerged as the dominant exposure pathway for SARS-CoV-2 transmission, much of what was promoted from CFD was applied to risk models to estimate community infection and in some cases expected clinical outcome. COVID-19 proved to fit the profile of an obligate respiratory-transmitted pathogen, and the plausibility of using aerosol modeling when silhouetted with emerging COVID-19 epidemiology provided ample evidence for promotion of masking and ventilation optimization as a required public health measure. And overall, masking and other forms of respiratory protective measures have been successful in suppressing viral infection. Masking is often included as a factor in developed risk models and it remains an essentially important part of our response to this airborne threat, and ultimately will agnostically J o u r n a l P r e -p r o o f Journal Pre-proof reduce disease burden although efforts to improve ventilation in indoor spaces remain a challenge. Arguably the most important concept in the airborne transmission of infectious agents is the biologically active componentry that comprises the aerosol particle and the functional dynamic nature of particle contents. Specifically, the innate generation, transport, and ultimate deposition/disposition of bioaerosols; the aerosol particles that nearly exclusively harbor bioactive components, including viruses, when disease agents are transmitted through the air. The difficulty to understand, modelize and predict the biological aspect of transmission has led to sometimes simplified approaches. Adding the biological perspective into the interpretation of models and capturing the breadth of biological variables and the complexity of predicting the behavior of viral aerosols and their consequences is an important part of transdisciplinary communication. Bioaerosols are aerosol particles that harbor a constellation of biologic componentry packaged on a microbial scale. It is now widely accepted that biologically active agents when in aerosol form rarely travel through the air in a singular state. Rather, when viruses are propelled into the air through natural generation processes directly from the respiratory system (e.g., exhaled breath, cough, sneeze) or through fomite re-aerosolization in cases where viruses can maintain upon inanimate surfaces, they are carried on particles on which their own size have negligible impact. In the case of the former, the composition of the aerosol particle is liquid, and its potentially pathogenic componentry is susceptible to environmental manipulation once liberated from a warmed humidified respiratory system. The resulting plasticity of a hydrophobic (orscopic) ambient environment alters any residual protection from other environmental hazards such as ultraviolet radiation that may ultimately effect replication competence or water activity, salt concentration and changes in the pH of the aerosol particle 4 . Prevailing size can also be J o u r n a l P r e -p r o o f Journal Pre-proof affected during the transport process and change the overall trajectory of each particle depending upon the composition and relative density of the 'solute' or liquid carrier of the aerosol. The perspective of variable biochemical components and their impacts on bioaerosol fate is mostly lacking in the prediction models. Terminal settling velocity, or the time associated with settling to the ground in a theoretically static ambient environment, is the major force behind whether the bioaerosol particle travels more or less than the now-infamous 'six-foot' social distancing mimetic that has been followed for over two years now 5 . Because the particle size is contingent upon the environment in which it is produced and travels through, the replication competence of the virus can be affected by the shrinking (or expanding) of the aerosol particle that has consequences on viral structures integrity and potential for viral fusion. This phenomenon is everchanging based upon the interactions of the contagious individual, respective generation rate, and the environment into which these particles are generated, and has been noted as an important physiochemical change that ultimately effects infection potential 6 . Even the probability of virion presence within the aerosol particle has been theorized as being statistically functional as a Poisson distribution and thereby estimated to be present in only a very small percentage of total bioaerosols produced by someone clinically ill with the disease 7 . Infectious particles resulting from the process of natural aerosol generation can and as we know from the epidemiology of the current pandemic, possesses the capacity to be inhaled and induce Uniting Infectious Disease and Physical Science Principles on the Importance of Face Masks for COVID-19 How can airborne transmission of COVID-19 indoors be minimised? Estimation of airborne viral emission: Quanta emission rate of SARS-CoV-2 for infection risk assessment Aerobiology: Experimental Considerations, Observations, and Future Tools Aerosols should not be defined by distance travelled Mechanistic insights into the effect of humidity on airborne influenza virus survival, transmission and incidence Size distribution of virus laden droplets from expiratory ejecta of infected subjects Quantitative assessment of the risk of airborne