WHO debunks myths about the spread of airborne diseases. CDC may not respond.

The World Health Organization has released a report that will change the world's understanding of respiratory infections such as coronavirus disease (COVID-19), influenza and measles.

Motivated by major failures in the pandemic, WHO convened around 50 experts in specialized fields including virology, epidemiology, aerosol science and biotechnology to review the evidence on how airborne viruses and bacteria spread. We conducted a thorough investigation over the course of two years.

However, the WHO report stops short of prescribing actions that governments, hospitals and the public should take. It remains to be seen how the Centers for Disease Control and Prevention will act on this information in its own guidance on infection control in health care settings.

The WHO concluded that airborne transmission occurs when sick people exhale pathogens that remain airborne in particles of saliva or mucus that are inhaled by others.

While that may seem obvious, and some researchers have been advocating this understanding for more than a decade, another dogma persists, which is why health officials have been trying to keep up with the new coronavirus for months after the pandemic began. It could not be said that the coronavirus was transmitted through the air.

Specifically, it relied on the traditional concept that respiratory viruses spread primarily through droplets exhaled from an infected person's nose or mouth. These droplets infect others by landing directly on their mouths, noses, or eyes. Alternatively, the droplets can be carried into contaminated finger orifices. While these routes of transmission still occur, especially among young children, experts believe that many respiratory infections are spread by people simply breathing virus-laden air. I am concluding.

“This is a complete about-face,” said Julian Tan, a clinical virologist at the University of Leicester in the UK who advised the WHO on the report. He also helped create an online tool to assess the risk of indoor airborne transmission.

Peg Seminario, an occupational safety and health expert in Bethesda, Maryland, welcomed the shift after years of resistance from health officials. “The established theory that droplets are the main route of infection has now become the 'Earth is flat' position,” she says. “Hooray! We are finally realizing that the world is round.”

The changes re-emphasize the need to improve indoor ventilation and stockpile high-quality masks before the next outbreak of airborne diseases. Measles cases are on the rise this year, and it is not unlikely that H5N1 avian influenza is circulating among cattle in some states. Scientists are concerned that as the H5N1 virus spends more time inside mammals, it could evolve to more easily infect people and spread between people through the air. .

Traditional thinking about droplet transmission helps explain why the WHO and CDC placed such emphasis on hand-washing and surface cleaning early in the pandemic. Such advice overrode recommendations for N95 masks, which filter out most airborne virus-laden particles. Employers have denied many healthcare workers access to N95s, arguing that only those who routinely work in front of coronavirus patients need them. More than 3,600 healthcare workers died in the first year of the pandemic, many due to lack of protection.

But the committee advising the CDC appears poised to ignore the latest science when it comes to pending guidance on medical facilities.

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

“Rubber faces challenges when deciding how to protect people,” Brosseau said. “Aerosol scientists may see this report as a big victory because they think everything will be science-based. But this is not the case and there are still significant barriers.”

Money is one thing. This means that when respiratory illnesses are spread by inhalation, the risk of infection indoors can be lowered by using potentially expensive air purification methods, such as artificial ventilation, using air purifiers, and wearing N95 masks. To do. The CDC has so far been reluctant to require such measures as it updates basic guidelines for controlling airborne transmission 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.

The WHO report does not characterize whether airborne viruses and bacteria travel short or long distances, but the CDC draft retains these traditional categories. For pathogens that are “mainly spread over short distances,” he prescribes looser-fitting surgical masks instead of N95s. Surgical masks block far fewer airborne virus particles than N95s, which are about 10 times more expensive.

Researchers and health care workers are outraged by the committee's draft proposal and have submitted letters and petitions to the CDC. They say it misunderstands the science and risks health. “The separation between short and long range is completely artificial,” Tan said.

Airborne viruses travel in the same way as cigarette smoke, he explained. The scent will be strongest near the smoker, but if someone further away remains in the room, they will inhale more smoke, especially if there is no ventilation.

Similarly, people open their windows when making toast and the smoke fills the kitchen and dissipates before an alarm can be sounded. “Do you think the virus stops at three feet and falls to the ground?” Tan said of the classic distance concept. “That's unreasonable.”

Although the CDC's advisory committee is primarily made up of infection control researchers from large hospital systems, the WHO consulted a diverse group of scientists considering different types of studies. For example, one analysis looked at clouds of fog exhaled by singers and musicians playing clarinet, French horn, saxophone, and trumpet. Other researchers reviewed 16 studies of COVID-19 outbreaks in restaurants, gyms, food processing plants, and other facilities and found that poor ventilation led to worse-than-normal outbreaks. I discovered that it is possible.

In response to the outcry, the CDC sent the draft document back to the committee for consideration and asked it to reconsider its recommendations. Since then, meetings of the expanded working group have been held behind closed doors. However, the American Federation of Nurses union obtained notes of the conversation through a public records request to the agency. The record suggests a push for looser protections. According to notes from the committee's March 14 discussion, one anonymous committee member said, “As far as compliance is concerned, it may be difficult not to make surgical masks an option.” “Supply and compliance will be difficult,” another official warned.

Far from echoing such concerns, the Nurses Union states on its website that “working groups prioritize employer costs and benefits (often under the umbrella of 'feasibility' and 'flexibility') over strong protections. ),” he wrote. Jane Thomasson, the union's chief industrial hygienist, said the meeting notes suggest the CDC group is working in the opposite direction, shaping the definition of airborne transmission to fit their desired outcomes. .

Mr Tan expects resistance to the WHO report. “Infection control people who have built their careers on this will probably disagree,” he said. “It takes a long time to change people's mindset.”

The CDC declined to comment on how the WHO transition will affect final policy on infectious disease control in health care facilities, which may not be completed by the end of the year. Developing policies to protect people from inhaling airborne viruses is complicated by the many factors that influence how the virus spreads indoors, including ventilation, temperature, and the amount of space.

Adding to the complexity, policymakers will need to weigh the burden of protection against the harm of a range of diseases, from the coronavirus to the common cold to tuberculosis. Additionally, fees often vary depending on the circumstances, such as whether the outbreak occurred in a school or a cancer ward.

“What is the level of mortality that people will accept without precautions?” Tang said. “That's another question.”