They knew: the CDC is well aware of aerosol transmission and the ways to protect people from infectious disease using respirator masks and the precautionary principle.
Remember this? https://www.politico.com/news/2020/03/27/republican-fundraiser-company-coronavirus-152184
Aerosol transmission & respirator masks, a PPE timeline
Remember this? https://www.politico.com/news/2020/03/27/republican-fundraiser-company-coronavirus-152184