Friday 18 September: CDC posted information on its website that for the first time said covid-19 could be spread through “respiratory droplets or small particles, such as those in aerosols, produced when an infected person coughs, sneezes, sings, talks, or breathes. These 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.” “There is growing evidence that droplets and airborne particles can remain suspended in the air and be breathed in by others and travel distances beyond 6 feet (for example, during choir practice, in restaurants, or in fitness classes). In general, indoor environments without good ventilation increase this risk.”
Monday 21 September: CDC removed the information about aerosols and distances greater than 6 feet (1.8 m) and replaced it with previous information that warned only about droplets and advised people to stay 6 feet apart [Ref-1].The CDC said that a draft version of proposed changes had been posted in error. The agency said it was updating information about airborne transmission of covid-19 and would post the new information once the review was completed.
The suggestion that covid-19 could be spread by aerosols, which can hang in the air for hours and spread over distances, has implications. As colder weather will force people indoors, concerns are rising about increased transmission in enclosed spaces and the efficacy of ventilation.
In July two scientists published a commentary in Clinical Infectious Diseases saying it was time “to recognize the potential for airborne spread … There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale) and we are advocating for the use of preventive measures.” [Ref-3] “We need to do something beyond 6 feet.” She said that meant masks and ventilation and filtration.5