The top U.S. public health agency said Monday that the coronavirus can spread more than 6 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 CDC 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 6 feet apart.