clinical assessment affect the generalizability of ASI estimates . Greater care and standardization with case definitions is justified to avoid misinterpretation of research findings , as occurred when a high rate of “ undocumented infection ” ( 86 percent )— apparently an admixture of ASIs , unreported symptomatic infections , and undiagnosed mild infections — was reported to be the source of 79 percent of documented cases . This was misconstrued across scientific papers and social networks as ASI being responsible for most SARS-CoV-2 infections .”
Droplet vs . aerosol transmission of SARS-CoV-2
The fourth false dichotomy is the current debate over droplets and aerosols , particularly relating to their size and the distance they can travel . Definitions from engineers studying the mechanics of air flow differ from those issued from within the healthcare sector , and as Escandón , et al . ( 2021 ) point out , “ Droplets and aerosols are erroneously seen as categorical transmission modes instead of a continuum of respiratory particles influenced by particle size and density , emission composition , turbulence and direction of the exhaled jet plume , and interacting environmental conditions . Larger droplets ( traditionally defined as > 5 – 10 μm in diameter ) stay aloft for shorter periods of time relative to their size , settle on the ground within seconds to minutes because of gravitational force , and are transmitted over short distances ( usually less than 6 feet ), although airflow can propel them farther across a room . Small-particle aerosols or droplet nuclei ( traditionally defined as < 5 μm ) generally evaporate and disperse faster than they fall , remain in the air for minutes to hours , and travel longer distances . This outdated distinction between droplets and aerosols has been revised by aerosol scientists arguing that the correct size threshold to differentiate these particles should be 100 – 200 μm . ‘ Aerosols ,’ a term commonly used as a shorthand for “ aerosol particles ,” are defined as a stable suspension of solid and / or liquid particles in air smaller than the above size cutoff , whereas droplets are defined as liquid particles larger than aerosols .” ( NOTE : For recent coverage of this topic , see the 2021 SHEA Decennial special edition at : https :// www . healthcarehygienemagazine . com / special-editions /)
The evidence supports that aerosol-generating behaviors such as coughing , sneezing , speaking , singing , shouting , breathing , as well as and medical aerosol-generating procedures ( AGPs ) lead to the production of respiratory particles spanning a wide spectrum of sizes . Scientists also know that SARS-CoV-2 transmission depends on factors including inoculum , virus viability , exposure distance and duration , environmental factors , and host factors . What becomes problematic , Escandón , et al . ( 2021 ) note , is that “ Airborne transmission — taken in its traditional definition of long-distance and respirable aerosols — is not the dominant or exclusive route for SARS-CoV-2 transmission . Conflicting and polarizing messages pertaining to SARS-CoV-2 transmission modes jeopardize pandemic response plans , resulting in public unwillingness to adhere to risk-reduction practices . Exaggerating the frequency of a transmission route prioritizes unnecessary IP & C
measures and social behaviors in hospital and community settings at the expense of effective interventions in place and undercuts public trust . Infectious disease transmission has important implications for deploying cost-effective IPC protocols and allocating resources to achieve the largest impact possible . Overstated evidence can lead to harmful policies . By amplifying findings from studies with methodological concerns and limited transferability of results , some academics and laypeople have advocated the use of filtering facepiece respirators ( FFRs ) in routine healthcare or even in community scenarios , despite evidence showing that FFRs may not be necessary in some settings to reduce transmission risk . This has led to risk perception disparities and public confusion .”
When evaluating the evidence regarding SARS-CoV-2 transmissions mechanics , the authors caution that while epidemiological data – such as outbreak , cohort , and case-control studies – help determine SARS-CoV-2 transmission mechanisms in real-world conditions , the studies that report on theoretical modeling or laboratory-based data are useful but may not reflect the frequency of a transmission mode and the real-life situations , “ especially if they
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Conflicting and polarizing messages pertaining to SARS-CoV-2 transmission modes jeopardize pandemic response plans , resulting in public unwillingness to adhere to risk-reduction practices .
do not consider SARS-CoV-2 infectivity or are simulated in vastly different scenarios ,” they say .
The authors also object to the lack of nuance around use of the term “ airborne ” that encompass and specialized meanings referring to long-distance aerosol-based transmission : “ While some scientists advocate the use of the term ‘ airborne ’ as a simple term to use in risk communication with the public , the plain usage of this word when referring to SARS-CoV-2 transmission is technically reductionist and ambiguous . The flagrant use of the term ‘ airborne ’ without providing nuance can be misinterpreted . For example , if the public wrongly believes that transmission occurs overwhelmingly from aerosols over an extended distance and time , they may reject guidance to wear medical masks or cloth face coverings ( given their limited aerosol filtering efficiency in comparison with other facepieces ), hoard FFRs , or feel that distancing precautions are futile . Likewise , if the public believes that the virus spreads extensively in the outdoor air and travels down blocks or across buildings , this may lead to potentially dangerous practices such as closing all windows in residential areas .”
They continue , “ From a public health standpoint , the term ‘ airborne ’ is not actionable on its own because it offers no clear guidance on how to curtail exposure risk . Simplistic messages and press article headlines , such as ‘ The coronavirus is airborne ’ … require nuance to provide effective and accurate risk communication in public health and to avoid misunderstandings of viral transmission and airborne fearmongering . This has been exacerbated by scientific commentaries claiming with selective citations that airborne transmission is the predominant mode