New WHO Terminology to Clear Confusion over ‘Airborne’ Pathogens

The World Health Organization (WHO) has published a new technical report including updated terminology to describe pathogens that are transmitted through the air, following “an extensive, multi-year, collaborative effort”.

It follows confusion and contestation between scientists during the COVID-19 pandemic because of the “varying terminologies” and  “gaps in common understanding”, said the WHO.

These “contributed to challenges in public communication and efforts to curb the transmission of the pathogen”.

However, a number of scientists called out the WHO itself for being slow to acknowledge that SARS-CoV2 could be transmitted in the air.

“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’s 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.”

Experts and four major public health agencies – the Africa Centres for Disease Control Prevention, Chinese Center for Disease Control and Prevention, European Centre for Disease Prevention and Control and US Centers for Disease Control and Prevention – were consulted between 2021 and 2023.

Away with ‘aerosols’ and ‘droplets’

Instead of ‘aerosols’ and ‘droplets’, the report uses the new descriptor, ‘infectious respiratory particles’ (IRPs), describing these as existing “on a continuous spectrum of sizes, and no single cut-off points should be applied to distinguish smaller from larger particles”. 

This facilitates a “away from the dichotomy of previously used terms: ‘aerosols’ (generally smaller particles) and ‘droplets’ (generally larger particles)”.

These IRPs are transmitted by people infected by a respiratory pathogen “through their mouth or nose by breathing, talking, singing, spitting, coughing or sneezing”. 

‘Through the air’

Under the umbrella of ‘through the air’ transmission, the report advises the use of two descriptors. The first is “airborne transmission or inhalation” for cases when IRPs are expelled into the air and inhaled by another person, who could be at quite a distance from the infected person.

The second is “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.

The pathogens covered include those that cause respiratory infections, such as COVID-19, influenza, measles, Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and tuberculosis.

Image Credits: Towfiqu Barbhuiya/ Unsplash.

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