Global Technical Consultation Report on Proposed Terminology for Airborne Pathogens

The terminology used to describe the transmission of pathogens through the air varies by scientific discipline, organization, and general public. While this has been the case for decades, during the coronavirus disease (COVID-19) pandemic, the terms “airborne transmission,” “airborne transmission,” and “aerosol transmission” have been used in different scientific fields. It was used in different ways by different stakeholders. This contributed to misleading information and confusion about how the pathogen is transmitted within the human population.

This global technical consultation report aims to seek consensus on the terminology used to describe the transmission of pathogens through the air that can cause human infection. We compile opinions from experts across fields.

This consultation aimed to identify terminology that would be understood and accepted in various technical fields. The agreed process was to produce a consensus document that could be endorsed by global institutions and bodies. Despite complex debates and challenges, this consultation process resulted in agreement on a set of descriptors to describe, among other things, how pathogens are transmitted through the air and associated modes of transmission; Significant progress has been made. WHO is aware of important areas where agreement was not reached and will continue to address these areas in follow-up consultations.

Range of pathogen types covered in this consultation and resulting descriptors The ones used in this document are:

• Pathogens contained within particles (known as “infectious particles”). These infectious particles travel through the air when carried by the exhaled breath stream (known as “infectious respiratory particles” or IRPs) and enter the human respiratory tract. tubes (or deposited in the mucous membranes of another person's mouth, nose, or eyes) and;
• Pathogens from any source (including humans, animals, and the environment) that primarily cause respiratory infections (such as tuberculosis) [TB]influenza, severe acute respiratory syndrome [SARS]Middle East Respiratory Syndrome [MERS]), but also infections that cause infections involving the respiratory system or other organ systems (e.g., COVID-19, measles).

Global Technical Consultation Report on Proposed Terminology for Airborne Pathogens

The following descriptors and stages are defined by this extensively discussed consultation to characterize airborne pathogen transmission (under typical circumstances).

• A person infected with a pathogen may produce pathogen-containing particles along with water and respiratory secretions during the contagious (source) stage of the disease. Such particles are described herein as potentially “infectious particles.”
• These potentially infectious particles are carried by the exhaled air stream and exit the infected person's mouth/nose and enter the surrounding air through breathing, talking, singing, spitting, coughing, and sneezing. In this respect, these particles are known as “infectious respiratory particles” or IRPs.
• IRPs exist in a variety of sizes (from submicron to millimeter diameters). The emitted IRP is exhaled as a puff cloud (first moving independently of the airflow and then further dispersed and diluted by background air movement in the room).
• IRPs exist on a continuous spectrum of sizes, and there is no need to apply a single cutoff point to distinguish between small and large particles. This allows us to move away from the previous dichotomy of terms known as 'aerosols' (generally small particles) and 'droplets'. (generally larger particles).
• Many environmental factors influence the way IRPs move through the air, including ambient temperature, speed, humidity, sunlight (ultraviolet radiation), airflow distribution in the space, and many other factors, and may affect how IRPs travel through the air and reach other individuals. This affects whether the IRP remains viable and infectious when infected.

The descriptor “airborne” can be used in a general way to characterize infectious diseases in which the primary route of transmission involves the pathogen traveling through the air or becoming airborne. It has similarities to other public health descriptors for infectious diseases, such as “waterborne” and “bloodborne,” which refer to the primary medium by which a particular disease is transmitted, and is widely used in the scientific, clinical, public health, and scientific communities. is commonly understood. general citizen.

The descriptor “airborne transmission” can be used to describe the mode of transmission of an IRP over the air.

Two descriptors can be used under the umbrella of “through the air.”

• 'Airborne/Inhalation': This occurs when IRP released into the air as described above enters the respiratory tract of another person through inhalation, potentially causing an infection. This form of infection can occur when IRP travels short or long distances from an infected person. Although the entry point for her IRPs into respiratory tract tissues during airborne infections could theoretically occur at any point along the human airway, the preferred entry site may be pathogen-specific. . Note that travel distance depends on multiple factors, including particle size, emission mode, and environmental conditions (airflow, humidity, temperature, settings, ventilation, etc.).
• '“Direct vapor deposition”: IRPs are released into the air following short-range semi-ballistic trajectories and are then deposited directly onto other people's exposed facial mucosal surfaces (mouth, nose, eyes) and enter the human respiratory tract through these entry points. enter and potentially occur. cause infection.