Is it standard protocol at MCF's to ask that family stay away due to several residents being ill, to avoid germs from spreading?

There are several residents at moms MCF that are sick with a bug and when I went to visit mom last night they had posted a note on the door stating as much and to "Steer Clear (4 days) to avoid the germs...", They also state if you do go in, to wash hands and use masks before entering. I appreciate the heads up, and the mask. However, I (many family members) of residents go visit our Loved Ones (LO) everyday so haven't we already been exposed to the bug? Should I really stay away? I was just wondering if anyone knows if this is standard protocol at a Memory Care Facility. Thanks in advance.