The top US public health agency has said that the coronavirus can spread more than six feet through the air, especially in poorly ventilated and enclosed spaces. But agency officials maintained that such spread is uncommon and current social distancing guidelines still make sense.

However, several experts faulted the updated Centers for Disease Control and Prevention guidance. They said the virus can spread more easily than the CDC seems to be indicating, and suggested that the public should wear masks even in prolonged outdoor gatherings when they are more than six feet apart.

In the update posted on its website, the agency again acknowledged recent research showing people with Covid-19 infected others who were more than six feet away or shortly after an infected person left an area. CDC officials called those ”limited, uncommon circumstances”.

In those cases, spread occurred in poorly ventilated and enclosed spaces where people were doing activities that caused heavier breathing, like singing or exercise, CDC officials said.