#18,015
Although we've seen similar debates with other outbreaks, during the opening months of the COVID pandemic there was much disagreement (see COVID-19: The Airborne Division) over whether SARS-CoV-2 was an `airborne' virus, and what levels of personal protections (masks/gowns/gloves/eye protection) were appropriate for medical workers and for the public.
Six months into the crisis, 200+ scientists from around the world signed an open letter to the WHO, urging them to reconsider their stance on the airborne spread of the virus.It is Time to Address Airborne Transmission of COVID-19
Lidia Morawska, Donald K Milton
Clinical Infectious Diseases, ciaa939, https://doi.org/10.1093/cid/ciaa939
While the CDC had recommended `airborne precautions' for health care workers (when possible) since the beginning of this epidemic (see J. Infect. Dis.: Airborne or Droplet Precautions For COVID-19?), their guidance on how the virus spread in the community focused more on large droplet (short-range and short-lived) spread of the virus and contaminated fomites, rather than on aerosols.
Hence early messaging discouraging the use of face masks for the public (partially reversed on Apr. 4th, 2000).
A large part of the problem was semantics. Scientists and policy makers couldn't agree on what constituted `airborne' transmission, resulting in mixed and confused messaging.
While today it is widely accepted that COVID is highly transmissible via the respiratory route (see EID Journal: Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021), we can't afford to go through this same protracted debate with every new pathogen.
Although it has taken 4 years and countless committee meetings, yesterday WHO released a 52-page report on redefining the terminology that describes pathogens that transmit through the air.
First the press release from the WHO, followed by a link and a few brief excerpts from the document.
Leading health agencies outline updated terminology for pathogens that transmit through the air
18 April 2024
News release
Reading time: 3 min (692 words)
Following consultation with public health agencies and experts, the World Health Organization (WHO) publishes a global technical consultation report introducing updated terminology for pathogens that transmit through the air. The pathogens covered include those that cause respiratory infections, e.g. COVID-19, influenza, measles, Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and tuberculosis, among others.
The publication, entitled “Global technical consultation report on proposed terminology for pathogens that transmit through the air”, is the result of an extensive, multi-year, collaborative effort and reflects shared agreement on terminology between WHO, experts and four major public health agencies: Africa Centres for Disease Control and Prevention; Chinese Center for Disease Control and Prevention; European Centre for Disease Prevention and Control; and United States Centers for Disease Control and Prevention. This agreement underlines the collective commitment of public health agencies to move forward together on this matter.
The wide-ranging consultation was conducted in multiple steps in 2021-2023 and addressed a lack of common terminology to describe the transmission of pathogens through the air across scientific disciplines. The challenge became particularly evident during the COVID-19 pandemic as experts from various sectors were required to provide scientific and policy guidance. Varying terminologies highlighted gaps in common understanding and contributed to challenges in public communication and efforts to curb the transmission of the pathogen.
“Together with a very diverse range of leading public health agencies and experts across multiple disciplines, we are pleased to have been able to address this complex and timely issue and reach a consensus,” said Dr Jeremy Farrar, WHO Chief Scientist. “The agreed terminology for pathogens that transmit through the air will help set a new path for research agendas and implementation of public health interventions to identify, communicate and respond to existing and new pathogens.”
The extensive consultation resulted in the introduction of the following common descriptors to characterize the transmission of pathogens through the air (under typical circumstances):
Individuals infected with a respiratory pathogen can generate and expel infectious particles containing the pathogen, through their mouth or nose by breathing, talking, singing, spitting, coughing or sneezing. These particles should be described with the term ‘infectious respiratory particles’ or IRPs.
IRPs exist on a continuous spectrum of sizes, and no single cut off points should be applied to distinguish smaller from larger particles. This facilitates moving away from the dichotomy of previously used terms: ‘aerosols’ (generally smaller particles) and ‘droplets’ (generally larger particles).
The descriptor ‘through the air’ can be used in a general way to characterize an infectious disease where the main mode of transmission involves the pathogen travelling through the air or being suspended in the air. Under the umbrella of ‘through the air transmission’, two descriptors can be used:
1. Airborne transmission or inhalation, for cases when IRPs are expelled into the air and inhaled by another person. Airborne transmission or inhalation can occur at a short or long distance from the infectious person and distance depends on various factors (airflow, humidity, temperature, ventilation etc). IRPs can theoretically enter the body at any point along the human respiratory tract, but preferred sites of entry may be pathogen-specific.
2. Direct deposition, for cases when IRPs are expelled into the air from an infectious person, and are then directly deposited on the exposed mouth, nose or eyes of another person nearby, then entering the human respiratory system and potentially causing infection.
“This global technical consultation process was a concerted effort of many influential and experienced experts,” said Dr Gagandeep Kang, Christian Medical College, Vellore, India who is a Co-Chair of the WHO Technical Working Group. “Reaching consensus on these terminologies bringing stakeholders in an unprecedented way was no small feat.
Completing this consultation gives us a new opportunity and starting point to move forward with a better understanding and agreed principles for diseases that transmit through the air,” added Dr Yuguo Li from the University of Hong Kong, Hong Kong SAR (China), who also co-chaired the Technical Working Group.
This consultation was the first phase of global scientific discussions led by WHO. Next steps include further technical and multidisciplinary research and exploration of the wider implementation implications of the updated descriptors.
The WHO overview, and a link to the PDF follows:
Overview
Terminology used to describe the transmission of pathogens through the air varies across scientific disciplines, organizations and the general public. While this has been the case for decades, during the coronavirus disease (COVID-19) pandemic, the terms ‘airborne’, ‘airborne transmission’ and ‘aerosol transmission’ were used in different ways by stakeholders in different scientific disciplines, which may have contributed to misleading information and confusion about how pathogens are transmitted in human populations.
This global technical consultation report brings together viewpoints from experts spanning a range of disciplines with the key objective of seeking consensus regarding the terminology used to describe the transmission of pathogens through the air that can potentially cause infection in humans.
This consultation aimed to identify terminology that could be understood and accepted by different technical disciplines. The agreed process was to develop a consensus document that could be endorsed by global agencies and entities. Despite the complex discussions and challenges, significant progress was made during the consultation process, particularly the consensus on a set of descriptors to describe how pathogens are transmitted through the air and the related modes of transmission. WHO recognizes the important areas where consensus was not achieved and will continue to address these areas in follow-up consultations.
From the report, we get the following graphical summary.
The WHO also adds the following caveat about the immediate practical implications of these changes.
There is NO suggestion from this consultative process that to mitigate the risk of short range airborne transmission full ‘airborne precautions’1 (as they are currently known) should be used in all settings, for all pathogens, and by persons with any infection and disease risk levels where this mode of transmission is known or suspected (126).
But conversely, some situations will require ‘airborne precautions’. This would clearly be inappropriate within a riskbased infection prevention approach where the balance of risks, including disease incidence, severity, individual and population immunity and many other factors, need to be considered, inclusive of legal, logistic, operational and financial consequences that have global implications regarding equity and access.
While these changes should help streamline the conversation, we'll have to wait to see what practical effect they will have on the issuance of guidance on infection protection against novel disease threats going forward.
