The World Health Organization breaks down dogma about airborne diseases, but the CDC may not act on it • Daily Montanan

The World Health Organization has published a report that transforms the way the world understands respiratory infections like COVID-19, flu and measles.

Motivated by serious mistakes in the pandemic, the WHO brought together about 50 experts in virology, epidemiology, aerosol science and bioengineering, among other specialties, who spent two years studying the evidence on how airborne viruses and bacteria spread.

However, the WHO report does not prescribe actions that governments, hospitals and the public should take in response. It remains to be seen how the Centers for Disease Control and Prevention will act on this information in its own guidance for controlling infections in health care settings.

The WHO concluded that airborne transmission occurs when sick people exhale pathogens that remain suspended in the air, contained in small particles of saliva and mucus that are inhaled by other people.

While it may seem obvious, and some researchers have pushed for this recognition for more than a decade, an alternative dogma persisted – one that prevented health authorities from saying that COVID-19 was airborne for many months after the pandemic.

Specifically, they were based on the traditional notion that respiratory viruses spread primarily through droplets expelled from the nose or mouth of an infected person. These droplets infect others by landing directly in the mouth, nose or eyes – or are carried to these orifices on fingers contaminated with droplets. Although these transmission routes still occur, especially among young children, experts have concluded that many respiratory infections spread when people simply breathe in virus-laden air.

“This is a complete turnaround,” said Julian Tang, a clinical virologist at the University of Leicester in the United Kingdom who advised the WHO on the report. He also helped the agency create an online tool to assess the risk of airborne transmission indoors.

Peg Seminario, an occupational health and safety specialist in Bethesda, Maryland, welcomed the change after years of resistance from health officials.

“The dogma that droplets are the primary mode of transmission is the current ‘flat Earth’ position,” she said. “Alive! We are finally recognizing that the world is round.”

The change puts new emphasis on the need to improve indoor ventilation and stockpile quality face masks before the next airborne disease explodes. Far from a remote possibility, measles is on the rise this year and H5N1 bird flu is spreading among livestock in several states. Scientists fear that as the H5N1 virus spends more time in mammals, it could evolve to infect people more easily and spread between them through the air.

Traditional beliefs about droplet transmission help explain why the WHO and CDC focused so intensely on handwashing and surface cleaning early in the pandemic. Such advice surpassed recommendations for N95 masks that filter out most airborne virus-laden particles. Employers denied many healthcare workers access to N95s, insisting that only those who routinely work near COVID-19 patients needed them. More than 3,600 healthcare professionals died in the first year of the pandemic, many of them due to a lack of protection.

However, a committee advising the CDC appears prepared to set aside up-to-date science when it comes to its pending guidance on health care facilities.

Lisa Brosseau, an aerosol expert and consultant at the Minnesota Center for Infectious Disease Research and Policy, warns of a repeat of 2020 if that happens.

“The rubber hits the road when you make decisions about how to protect people,” Brosseau said. “Aerosol scientists can see this report as a huge victory because they think everything will now come down to science. But that’s not how it works and there are still big barriers.”

Money is one of them. If a respiratory disease spreads through inhalation, this means that people can reduce the risk of infection indoors through sometimes expensive methods of cleaning the air, such as mechanical ventilation and the use of air purifiers, as well as use of an N95 mask. So far, the CDC has been reluctant to push for such measures as it updates key guidelines on reducing airborne infections in hospitals, nursing homes, prisons and other facilities that provide health care. This year, a committee advising the CDC released draft guidance that differs significantly from the WHO report.

While the WHO report does not characterize airborne viruses and bacteria as traveling short or long distances, the CDC draft maintains these traditional categories. She prescribes looser-fitting surgical masks, rather than N95s, for pathogens that “predominately spread over short distances.” Surgical masks block far fewer airborne viral particles than N95 masks, which cost about 10 times as much.

Researchers and health professionals were outraged by the committee’s bill, submitting letters and petitions to the CDC. They say this confuses science and puts health at risk.

“The separation between short-range and long-range distances is completely artificial,” Tang said.

Airborne viruses travel like cigarette smoke, he explained. The smell will be stronger next to a smoker, but anyone further away will inhale more and more smoke if they remain in the room, especially when there is no ventilation.

Similarly, people open the windows when burning toast to let the smoke dissipate before filling the kitchen and raising the alarm.

“Do you think viruses stop after one meter and fall to the ground?” Tang said about the classical notion of distance. “This is absurd.”

The CDC advisory committee is primarily made up of infection control researchers at large hospital systems, while the WHO consulted with a diverse group of scientists who analyze many different types of studies. For example, one analysis examined clouds expelled by singers and musicians playing clarinets, horns, saxophones, and trumpets. Another looked at 16 investigations into COVID-19 outbreaks at restaurants, a gym, a food processing plant and other locations, finding that poor ventilation likely made them worse than they would have been otherwise.

In response to the protests, the CDC returned the draft to its committee for review, asking it to reconsider its advice. Since then, meetings of an expanded working group have been held privately. But the National Nurses United union obtained notes of the conversations through a public records request to the agency. The records suggest a push for looser protection.

“It may be difficult, compliance-wise, not to have surgical masks as an option,” said an unidentified member, according to notes from the March 14 committee discussion. Another warned that “sourcing and compliance would be difficult.”

The nurses’ union, far from echoing such concerns, wrote on its website:

“The Working Group prioritized employer costs and profits (often under the umbrella of ‘feasibility’ and ‘flexibility’) over robust protections.” Jane Thomason, the union’s chief industrial hygienist, said meeting records suggest the CDC group is working backwards, shaping its definitions of airborne transmission to fit the outcome it prefers.

Tang expects resistance to the WHO report.

“The people who control infections and who have built their careers on it will object,” he said. “It takes a long time to change people’s way of thinking.”

The CDC declined to comment on how the WHO’s move might influence its final policies on infection control in healthcare facilities, which may not be finalized this year. Creating policies to protect people from inhaling airborne viruses is complicated by the number of factors that influence how they spread indoors, such as ventilation, temperature and space size.

Adding to the complexity, policymakers must weigh the cost of various diseases, from Covid-19 to colds and tuberculosis, against the burden of protection. And costs often depend on the context, for example, whether an outbreak occurs in a school or a cancer ward.

“What level of mortality will people accept without precautions?” Tang said. “That’s another question.”

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