It continued: "These particles can be inhaled into the nose, mouth, airways, and lungs and cause infection. CDC is now updating its recommendations regarding airborne transmission of SARS-CoV-2 (the virus that causes COVID-19)", it declared.
On Sunday, one of the lead authors of the letter, Donald Milton, a professor of environmental health at the University of Maryland who studies how viruses are transmitted, said the CDC's new language was a "major improvement".
The World Health Organization has not changed its policy on aerosol transmission of the coronavirus, it said on Monday after USA health officials published draft new guidance by mistake warning that it can spread through airborne particles.
Previously, the CDC page said that COVID-19 was thought to spread mainly between people in close contact - about 1.8m - and "through respiratory droplets produced when an infected person coughs, sneezes or talks".
While the CDC has not called for any new action to address the airborne threat of a virus that has now killed almost 200,000 Americans, experts said the change should help to shift policy and public behavior.
The Centers for Disease Control and Prevention said Monday that it made a mistake when it posted new guidance online citing "growing evidence" that COVID-19 is airborne, sending health experts and the public scrambling to determine if schools and business should rethink mitigation steps to prevent the spread of the virus.
The sudden veering away from widely accepted scientific guidance comes after months of scandal at the CDC, revolving around various episodes in which Trump administration appointees have contorted the agency's recommendations to match political exigencies. On Friday, the CDC quietly updated a page on its website on how the virus spreads.
"If you have been in close contact, such as within 6 feet of a person with documented SARS-CoV-2 infection for at least 15 minutes and do not have symptoms, you need a test", the CDC posted on its website Friday. Direction, ventilation, and intensity of airflow might affect virus transmission, even if social distancing measures and mask use are implemented according to current guidance.
"In general indoor environments without good ventilation increase this risk", the page added. "The best way to prevent illness is to avoid being exposed to this virus", it adds. Spread from touching surfaces is not thought to be the main way the virus spreads. In July, 239 scientists wrote to the World Health Organization and other public health institutes, urging them to be more open about the possibility that people could get infected by droplets that were floating in the air.
"Evidence has been accumulating for some time". The guidance also stated that these particles might travel further than six feet.