What is known about the aerial spread of coronavirus

on September 18The US Centers for Disease Control and Prevention has warned that small airborne particles, as well as large water droplets from sneezing and coughing, can infect others. It quoted growing “evidence”.

Along On September 21, the warning disappeared from the website, With a note that it was posted incorrectly and the CDC is updating recommendations.

This move puts the CDC in the midst of a debate about how the coronavirus infects people. The guidelines can make a difference by reopening restaurants, bars, and other places where people gather, sooner or later.

And it raised more questions about public health politics, and whether White House authorities are directing policy to health authorities.

So what does the science of aerial propagation really say?

The new situation is ongoing work, but many works show the potential for aerial propagation.

The challenge of proving aerial propagation

CDC Withdrawn language “There is increasing evidence that droplets and suspended particles can remain suspended in the air and be inhaled by others and travel more than 6 feet (for example, during chorus practice, restaurants, fitness classes, etc.) ). “

Why is this a big deal? This means that you may need to increase the guidelines for proper physical distance.

6 feet is a safety benchmark that has helped shape the reopening of schools and businesses across the country. This number is based on the long-standing finding that most of them fall to the ground in front of the 6-foot mark because the larger water droplets from the cough are so heavy.

However, much smaller droplets can hang in the air longer. The debate is whether they have enough virus to infect others. If the answer is yes, the impact on daily life can be significant.

Professor Donald Milton of the University of Maryland Medical School sees a lot of evidence that aerial propagation is a major factor, but emphasizes that it is difficult to get a definitive answer.

No one argues that being close to a sick person is the main threat. But Milton said it’s difficult to figure out what happens in the meantime.

“You can cough and get infected by hitting your eyes or mouth directly,” Milton said. “Alternatively, you may inhale through particles in the air, or you may have touched something and then your nose or mouth. It’s very difficult to sort out. “

However, many incidents and studies point to the idea that suspended particles play a larger role than expected.

research

Recently, an international group of researchers from China, Australia and the United States Review evidence of aerial propagation.. They concluded that it was very plausible.

Published in Minutes of the National Academy of Sciences Speaking loudly for one minute, it is reported that “1,000 droplet nuclei containing the virus are generated and can stay in the air for more than 8 minutes.”

What is the author’s conclusion? “These are more likely to be inhaled by others and therefore cause new infections.”

Public transport is an important test site.

In China, Scientists saw 126 passengers on two buses and traveled for about an hour and a half. One bus was not infected with the virus and the other bus had one infected rider. People on the bus were 41.5 times more likely to get the virus.

Many other researchers Superspreader event Two and a half hours of choral practice at Skagit Valley Chorale in Mount Vernon, Washington. Of the 61 attended, there were 53 confirmed potential cases and 2 deaths.

A University of Florida study Room air was sampled from two COVID patients. They found aerosol particles that carry enough viral load to infect people who are more than 15 feet away from the patient.

239 researchers in July Co-signed open letter It called on national and international health agencies to “recognize the potential for airborne diffusion” of COVID-19.

A credible study states that “the virus is undoubtedly released during exhalation, conversation, and coughing in microdroplets small enough to remain floating in the air and pose a risk of exposure. I showed it. “

Still, July World Health Organization Airborne transmission was reportedly possible, but more intense research was needed to confirm that it poses a significant risk.

If public health leaders take airborne transmission more seriously, Milton said there are several implications. Most business activities can continue, but restaurants and bars face higher hurdles because masks are not suitable for eating and drinking.

Beyond that, more attention to ventilation in more closed spaces is important, as is the supply of N95 masks.Those masks are still in short supply Supply..