Understanding the WHO's Updated Definition of Airborne Pathogens
Discover the latest clarification from the World Health Organization on airborne pathogens, now encompassing respiratory droplets spread through the air and landing on individuals. This expanded definition includes viruses like Covid-19, influenza, and measles, irrespective of droplet size. Stay informed on key updates in public health guidance.
The World Health Organization is expanding the definition of airborne pathogens to include when respiratory droplets spread through the air and land on a person, regardless of their size. WHO's new report aims to clarify how pathogens can potentially cause infection in humans through the air transmission.
The term "transmission through the air" is used to describe the spread of infectious respiratory particles through the air. This includes both "airborne transmission" and "direct deposition," as outlined in a recent WHO technical report developed with input from numerous scientists.
"Airborne transmission" occurs when infectious respiratory particles are expelled into the air, often through coughing or sneezing. These particles can then be inhaled by another person, entering their respiratory tract and potentially causing infection. On the other hand, "direct deposition" refers to infectious particles landing directly on a person's mouth, nose, or eyes, increasing the risk of infection.
Allissa Sanchez, LVN, gives her patient a vaccine during a flu and COVID-19 vaccination clinic at Kaiser Permanente Pasadena on October 12, 2023, in Pasadena, California.
Allissa Sanchez, LVN, gives her patient a vaccine during a flu and COVID-19 vaccination clinic at Kaiser Permanente Pasadena on October 12, 2023, in Pasadena, California.
Francine Orr/Los Angeles Times/Getty Images
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The World Health Organization states that these particles come in various sizes and can be spread over both short and long distances. This means that there is no specific size limit for particles under the updated terms.
"This report is significant as it will help improve communication with the public regarding the spread of pathogens and ways to minimize the risk of transmission," stated Linsey Marr, an aerosol scientist and professor at Virginia Tech, who is part of the consultation group responsible for the new report.
Marr explained, "Previously, a misunderstanding of how infectious diseases are transmitted through the air led to confusion about how Covid-19 spreads and how individuals could protect themselves. For instance, disinfecting groceries was not an effective use of our time." She added, "Health authorities were hesitant to acknowledge the term 'airborne' due to varying interpretations among experts. I believe that this report will empower public health communicators to use the term 'airborne' because it is the simplest and most straightforward way to explain to the general public how a disease can be spread."
The WHO report mentioned that the new term for airborne pathogens aligns with how other diseases are labeled, like "waterborne" or "bloodborne."
According to the report, the terms listed should be viewed as a foundation for more research, discussions, and funding in various fields.
In a video statement on Thursday, Jeremy Farrar, the chief scientist of WHO, highlighted the importance of the new report's terminology. He mentioned that the terminology can assist scientists from different fields in reaching a common understanding and clarity when discussing airborne pathogens.
Farrar emphasized that the document aims to unite various disciplines and establish a shared agreement. Regardless of whether one is an engineer, clinician, nurse, or public health professional, the use of terms like 'aerosol' and 'through the air' will convey the same meaning. He noted that the report covers a wide range of respiratory infections that are transmitted through the air, marking a significant moment in history.
The need for such consensus was evident at the peak of the Covid-19 pandemic.
‘There were many failures’
During the pandemic, there was confusion over terms used to explain how the coronavirus spreads, such as airborne, airborne transmission, or aerosol transmission.
“We noticed that experts from various fields were using different language to describe the same thing. This led to miscommunication and hindered collaboration,” Farrar explained.
SGMD Gupta Ebola not airborne_00002915.jpg
SGMD Gupta Ebola not airborne_00002915.jpg
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Around that same time, a group of scientists urged WHO to be more forthcoming about the likelihood that people can catch the virus from droplets floating in the air.
If the new WHO report had been available before the Covid-19 pandemic, public health officials might have labeled transmission as ‘airborne,’ recommended high-quality masks immediately, stressed the importance of good ventilation indoors, and decreased the focus on distancing and hand-washing, according to Marr.
The new report tackles a question that Dr. Jessica Justman, an infectious disease expert and professor of medicine in epidemiology at Columbia University Vagelos College of Physicians and Surgeons, found perplexing when Covid-19 first appeared - whether coronavirus aerosols or droplets played a more significant role in transmission.
"Respiratory particles come in various sizes, but for years we have categorized them as either aerosols or droplets based on a cut-off size of 5-10 microns," explained Justman in an email on Thursday. "I have always found this cut-off size arbitrary, and the new WHO report agrees. It suggests that we should no longer use a cut-off size and instead recognize the continuum of sizes."
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According to Stephen S. Morse, a professor of epidemiology at Columbia University Mailman School of Public Health, the new report is seen as an improvement. It helps to clarify the terminology that has been used for many years to describe airborne transmission involving larger and smaller particles. He mentioned this in an email on Thursday.
"Some agencies and scientists initially believed that the Covid-19 virus spread only through droplets, which do not travel as far as smaller particles. It was later recognized that both droplets and smaller particles can enable transmission. This is likely true for most, if not all, respiratory viruses, although the details may vary," explained Morse, who was not involved in the new WHO report.
Morse also pointed out that there were several failures in handling the pandemic. He mentioned that while greater clarity would have been helpful, he does not believe it would have significantly changed the outcome. Although clearer information could have assisted people in better protecting themselves, the lack of appropriate personal protective equipment was a hurdle regardless.
Editor's P/S:
The World Health Organization's (WHO) expanded definition of airborne pathogens is a significant step towards clarifying how respiratory infections can spread. By recognizing the continuum of particle sizes and acknowledging that infectious respiratory particles can land directly on a person's mouth, nose, or eyes, the new definition provides a more comprehensive understanding of airborne transmission. This will improve communication with the public and help individuals take appropriate measures to minimize their risk of infection.
The confusion over terminology during the COVID-19 pandemic highlights the need for a clear and consistent language. The new WHO report provides this clarity and can assist scientists, public health officials, and the general public in discussing airborne pathogens more effectively. It also underscores the importance of ongoing research and collaboration in the field of infectious disease transmission, as new evidence emerges and our understanding of how pathogens spread continues to evolve.
