On September 21, three days after CDC revised its guidance to acknowledge the spread of the novel coronavirus through aerosols and clearly mentioning that inhalation of particles, such as those in aerosols, is the “main way” the virus spreads, the nodal agency withdrew all mention of small particles and aerosols from the guidance.
In a terse message posted on the website containing the old guidelines, the CDC notes that a “draft version of proposed changes to these recommendations was posted in error to the agency’s official website”. It added that the agency is “currently updating its recommendations regarding airborne transmission of SARS-CoV-2 ” and will post the revised guidelines once the “process has been completed”.
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Compared with the July 9 guideline on coronavirus spread , the September 18 guidelines mentioned that in addition to respiratory droplets the virus is also spread through small particles, such as those in aerosols. The latest guidance posted on September 21 has no mention of small particles as possible carriers of the virus.
In addition to coughing, sneezing and talking, the September 18 guidelines mentioned breathing and singing as the possible ways by which droplets or particles are produced. But the September 21 guidelines has now removed the mention of breathing and singing as possible ways by which droplets or particles are produced.
The September 18 guidelines had also mentioned that the “particles can be inhaled into the nose, mouth, airways and lungs and cause infection. This is thought to be the main way the virus spreads”. In its place, the September 21 guidance now states that “droplets can land on the mouths or noses of people nearby or possibly inhaled into the lungs”.
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While the September 18 guidelines for the first time mentioned that there is “growing evidence that droplets and airborne particles can remain suspended in the air and be inhaled in by others, and travel distances beyond six feet” the September 21 guidelines has no mention of droplets and particles remining suspended in air and travelling to longer distances.
One possible reason why the September 18 guidelines were removed could be due to the ambiguity in the way the relative importance of different routes of transmission in virus spread. By stating that particles, which can be inhaled, is “thought to be the main way the virus spreads”, the guidance suggested that small particles such as aerosols play a predominant role in virus spread while transmission through droplets only had a relatively smaller role.
