WHO overturns dogma on the spread of airborne diseases. The CDC may not act on it.

The World Health Organization has published a report that transforms the way the world understands respiratory infections such as covid-19, influenza and measles.

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

However, the WHO report does not prescribe what actions 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 infection control in healthcare settings.

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 others.

While it may seem obvious, and some researchers have pushed for this recognition for more than a decade, an alternative dogma persisted, preventing health authorities from saying that covid was airborne for many months after the pandemic

Specifically, they were based on a traditional notion that respiratory viruses are spread primarily through droplets that are exposed from the nose or mouth of an infected person. These droplets infect others by landing directly in the mouth, nose, or eyes, or they are carried to these orifices by droplet-contaminated fingers. Although these routes of transmission still occur, especially among young children, experts have concluded that many respiratory infections are 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. It also helped the agency create an online tool to assess the risk of indoor airborne transmission.

Peg Seminario, an occupational health and safety specialist in Bethesda, Maryland, welcomed the change after years of resistance from health authorities. “The dogma that droplets are an important mode of transmission is now the ‘Flat Earth’ position,” he said. “Hooray! We are finally recognizing that the world is round.”

The change puts a new emphasis on the need to improve indoor ventilation and stock up on quality masks before the next airborne disease hits. 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 more easily infect people and spread between them through the air.

Traditional beliefs about droplet transmission help explain why the WHO and CDC focused so sharply on handwashing and surface cleaning at the start of the pandemic. That advice trumped recommendations for N95 masks that filter out most virus-laden particles suspended in the air. Employers denied many healthcare workers access to N95s, insisting that only those who routinely worked on the feet of covid patients needed them. More than 3,600 healthcare workers died in the first year of the pandemic, many due to a lack of protection.

However, a committee advising the CDC appears willing to ignore up-to-date science when it comes to its pending guidance on healthcare facilities.

Lisa Brosseau, an aerosol expert and consultant for the Minnesota Center for Infectious Disease Research and Policy, warns that it will happen again in 2020 if that happens.

“The rubber hits the road when decisions are made about how to protect people,” Brosseau said. “Aerosol scientists may see this report as a big win because they think everything will now follow from science. But that’s not the case and there are still big barriers.”

Money is one. If a respiratory disease is spread by inhalation, it means people can reduce their risk of infection indoors by using sometimes expensive methods of cleaning the air, such as mechanical ventilation and using air purifiers and the use of an N95 mask. So far, the CDC has been reluctant to push for such measures as it updates key guidelines to curb 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. It recognizes wider surgical masks instead of N95s for pathogens that “predominantly spread over short distances.” Surgical masks block far fewer airborne virus particles than N95s, which cost about 10 times more.

Researchers and health workers have been outraged by the committee’s draft, submitting letters and petitions to the CDC. They say the science is wrong and endangers health. “The separation between short-range and long-range distance is completely artificial,” Tang said.

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

Likewise, people open windows when burning toast to let the smoke dissipate before filling the kitchen and setting off the alarm. “Do you think viruses stop after 3 feet and fall to the ground?” Tang said of the classical notion of distance. “This is absurd.”

CDC’s advisory committee is made up primarily of infection control researchers from large hospital systems, while WHO consulted a diverse group of scientists who study many different types of studies. For example, one analysis looked at puff clouds expelled by singers and musicians playing clarinets, French horns, saxophones, and trumpets. Another reviewed 16 studies of covid outbreaks in restaurants, a gym, a food processing plant and other places, and found that insufficient ventilation likely made them worse than they otherwise would have been.

In response to the outcry, the CDC returned the draft to its committee for review, asking it to reconsider its advice. Since then, meetings of an expanded task force have been held privately. But the union National Nurses United obtained notes of the conversations through a public records request to the agency. The records suggest a push for looser protection. “It can be difficult in terms of compliance not to have surgical masks as an option,” said one unidentified member, according to notes from the committee’s March 14 discussion. Another warned that “supply and compliance would be difficult.”

The nurses’ union, far from echoing these concerns, wrote on its website: “The task force has prioritized employer costs and benefits (often under the umbrella of ‘feasibility’ and ‘flexibility’) over strong protections”. Jane Thomason, the union’s chief industrial hygienist, said the minutes of the meeting suggest the CDC group is working backwards, molding its definitions of airborne transmission to fit the outcome it prefers.

Tang expects resistance to the WHO report. “Infection control people who have built their careers on this will object,” he said. “It takes a long time to change the way people think.”

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

Adding to the complexity, policymakers must weigh the cost of various diseases, from covid to colds to tuberculosis, against the burden of protection. And the tolls often depend on the context, such as 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.”

Kaiser Health NewsThis article was reprinted from khn.org, a national newsroom that produces in-depth journalism on health issues and is one of the core operating programs of KFF, the independent source of research, polling and health policy journalism.

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